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Reproductive cycle of the purple snail Plicopurpura pansa (Gould 1853) from two locations at Baja California Sur, Mexico.



ABSTRACT The reproductive cycle reproductive cycle
n.
The cycle of physiological changes that begins with conception and extends through gestation and parturition.
 of purple snail, Plicopurpura pansa (Gould 1853), sampled randomly monthly over a period of 20 mo at Playa playa
 or pan or flat or dry lake

Flat-bottomed depression that is periodically covered by water. Playas occur in interior desert basins and adjacent to coasts in arid and semiarid regions.
 Cerritos at the Pacific, and Punta Perico at the Gulf of California Noun 1. Gulf of California - a gulf to the west of the mainland of Mexico
Sea of Cortes

Mexico, United Mexican States - a republic in southern North America; became independent from Spain in 1810
, Baja California Sur Baja California Sur (sr), state (1990 pop. 317,764), 27,571 sq mi (71,428 sq km), NW Mexico, on the Baja California peninsula. La Paz is the capital. , Mexico, was examined by histological his·tol·o·gy  
n. pl. his·tol·o·gies
1. The anatomical study of the microscopic structure of animal and plant tissues.

2. The microscopic structure of tissue.
 observations of the gonadal gonadal

pertaining to or arising from a gonad. See also testicular, ovarian.


gonadal cords
cords formed by epithelial cells which migrate from the mesonephric tubules in the embryo to the gonadal ridge and establish the indifferent
 development. At both sites year-round copulations were observed, whereas egg capsules could be found only during February to May. During nearly the whole period, male and female gonads were found in the developing stage. From January to July and August most female gonads were found in the ripe, and from January to June and August in the spawning stage. Male gonads in the spawning stage were observed from December to September. The recovering stage was found in male and female gonads between September and October. Synchronism synchronism /syn·chro·nism/ (sing´krah-nizm) synchrony.synchron´ic, syn´chronous

syn·chro·nism
n.
Coincidence in time; simultaneousness. Also called synchronia.
 of gonadal development between both sexes was evident. Spawning could be observed in females with a total shell length of more than 18 mm, whereas smaller animals had gonads in the developing stage. In gonads of males signs of spawning could be observed in animals larger than 18 mm. No relationship was found between the water temperature and the spawning period. The sex ratio was 1:1 at Playa Cerritos, whereas at Punta Perico more males than females were counted.

KEY WORDS: reproductive cycle, purple snail, Plicopurpura pansa, Muricidae

INTRODUCTION

Most marine snails of the family Muricidae, if not all, produce in the hypobranchial gland a colorless col·or·less  
adj.
1. Lacking color.

2. Weak in color; pallid.

3. Lacking animation, variety, or distinction; dull. See Synonyms at dull.
 secretion that turns on exposure to air and light to "Tyrian Purple" (Fretter & Graham 1994). For its dye the carnivorous car·niv·o·rous  
adj.
1. Of or relating to carnivores.

2. Flesh-eating or predatory: a carnivorous bird.

3.
, gonochoristic muricid Plicopurpura pansa (Gould 1853), which inhabits intertidal in·ter·tid·al  
adj.
Of or being the region between the high tide mark and the low tide mark.



in
 rocky shores Rocky shore is an intertidal area on seacoasts where solid rock predominates. Rocky shores are biologically rich environments, and make the ideal natural laboratory for studying intertidal ecology and other biological processes.  exposed to high impact waves of the open sea, has been exploited on the Pacific coast from Central America Central America, narrow, southernmost region (c.202,200 sq mi/523,698 sq km) of North America, linked to South America at Colombia. It separates the Caribbean from the Pacific.  to Mexico for hundreds of years by indigenous communities for dyeing threads of cotton to be woven afterwards into traditional dresses. However, in recent years in Mexico the commercial exploitation of the purple snail for dyeing kimonos with "Tyrian Purple" had reached such levels as to threaten the survival of the species, and in 1988 the Mexican government declared P. pansa a protected species (Anonymous 1988, 1994).

Despite the recent concerns about the state and recovery of P. pansa, little is known about the principal life-history features. The impeded accessibility, only during extreme low tides, is the main reason for the difficulties of P. pansa field research. Detailed information on the reproductive strategy however, is a prerequisite for the development of techniques for restocking natural populations and to facilitate effective management.

In Mexico, some information about the gonad gonad /go·nad/ (go´nad) a gamete-producing gland; an ovary or testis.gonad´algonad´ial

indifferent gonad  the sexually undifferentiated gonad of the early embryo.
 reproductive cycle of the purple snail P. pansa is available from Oaxaca (Hernandez-Cortes & Acevedo-Garcia 1987, Acevedo-Garcia et al. 1993), a histological study from Nayarit (Quiroz-Rocha 1992), and a detailed study about the reproductive cycle from Sinaloa (Gonzalez-Flores 1997). Especially, the understanding of the reproductive cycle and the spawning period of P. pansa will provide the necessary information needed for the determination of the recruitment period of natural populations. Up until now data are missing about the reproductive cycle of P. pansa from Baja California Sur, the most northern area of its distribution. The objectives of this study were to determine over a period of 20 mo the reproductive cycle of P. pansa at two locations in Baja California Sur. Additional information on minimum size at sexual maturity and sex ratio is needed to facilitate efficient management of this natural resource.

MATERIALS AND METHODS

Sampling

Preliminary trials were started from January to May 2000 to determine the best location and period for the collection of P. pansa, whether egg capsules can be found, and to assess the method of sampling to obtain statistically valid data. From intertidal rocks at days during extreme low-water spring tides at Playa Cerritos at the Pacific coast (23[degrees]19'54"N and 110[degrees]10'38"W) and at Punta Perico at the Gulf of California (24[degrees]01'54"N and 109[degrees]48'21"W; Fig. 1), 20-30 specimens from 100-300 animals of unexploited populations of P. pansa were randomly selected from June 2000 to January 2002, monthly, with the help of a table of random numbers. At Playa Cerritos a total of 592 were randomly selected during 20 mo and at Punta Perico a total of 596 specimens.

[FIGURE 1 OMITTED]

During sampling the water temperature was recorded, whether egg-capsules could be found and whether copulas were observed. Injecting a 10% neutral buffered formalin formalin /for·ma·lin/ (for´mah-lin) formaldehyde solution.

for·ma·lin
n.
An aqueous solution of formaldehyde that is 37 percent by weight.
 solution into the snails preserved the tissue of the animals. Subsequently about 24 h later in the laboratory the total SL of the animals was determined from the apex to the end of the siphon siphon (sī`fən, –fŏn), tube through which a liquid is lifted over an elevation by the pressure of the atmosphere and is then emptied at a lower level.  channel with the help of a digital caliper caliper

Instrument that consists of two adjustable legs or jaws for measuring the dimensions of material parts. Spring calipers have an adjusting screw and nut; firm-joint calipers use friction at the joint to hold the legs unmoving.
 with a precision of 0.01 mm, the shell was broken and the gonads and the digestive gland digestive gland
n.
A gland, such as the liver or pancreas, that secretes into the alimentary canal substances necessary for digestion.
 were removed. Table 1 shows the number of gonads examined, the average total SL with standard deviation In statistics, the average amount a number varies from the average number in a series of numbers.

(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers.
, and the size range. Sex determination was accomplished by visual inspection for a penis, and verified by histological examinations of the gonads.

Observations by Light Microscopy

The gonads were dehydrated de·hy·drate  
v. de·hy·drat·ed, de·hy·drat·ing, de·hy·drates

v.tr.
1. To remove water from; make anhydrous.

2. To preserve by removing water from (vegetables, for example).
 in the alcohol series, cleared with butylated hydroxanisole, and embedded Inserted into. See embedded system.  in paraffin paraffin, white, more-or-less translucent, odorless, tasteless, waxy solid. It melts between 47°C; and 65°C; and is insoluble in water but soluble in ether, benzene, and certain esters. . The sections (7-9-[micro]m thick) were prepared from the thickest part of the gonads, and subsequently, according to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

3.
 the methodology described by Luna (1968), stained with Harris hematoxylin hematoxylin /he·ma·tox·y·lin/ (he?mah-tok´si-lin) an acid coloring matter from the heartwood of Haematoxylon campechianum; used as a histologic stain and also as an indicator.  and contrasted with eosin eosin /eo·sin/ (e´o-sin) any of a class of rose-colored stains or dyes, all being bromine derivatives of fluorescein; eosin Y, the sodium salt of tetrabromofluorescein, is much used in histologic and laboratory procedures. . This method was adopted after verifying in four specimens, that gonadal maturity was uniform in different parts of the gonad. Both sexes were confirmed by light microscopic examination of histological preparations of the gonads. Light micrographs were taken with a digital camera (Olympus Camedia C-5060) mounted on a light microscope Noun 1. light microscope - microscope consisting of an optical instrument that magnifies the image of an object
binocular microscope - a light microscope adapted to the use of both eyes
 (Olympus BX 41).

Reproductive Cycle With Gonad Developmental Phases

To determine the seasonality and duration of the reproductive cycle from the histological preparations the development of the gonads The prenatal development of the gonads is a part of the development of reproductive system and sultimately forms the testes in males and ovaries in females. They initially develop from the mesothelial layer of the peritoneum.  is classified arbitrarily: in females it is divided into four successive stages (developing, ripe, spawning, recovering), in males only into 3 (developing, spawning, and recovering) stages.

Developing Stage

In female gonads in the developing stage can be found oogonia and developing oocytes (Photo la).The size of the gonads is increasing through the accumulation of growing ovocites accumulating yolk yolk (yok) the stored nutrient of an oocyte or ovum.

yolk
n.
The portion of the egg of an animal that consists of protein and fat from which the early embryo gets its main nourishment and of
. The oocytes are predominantly previttelogenic. In male gonads can be observed the spermatogenic spermatogenic /sper·ma·to·gen·ic/ (-jen´ik) producing semen or spermatozoa.

spermatogenic

giving rise to spermatozoa.
 follicles follicles,
n the masses that are embedded in a meshwork of reticular fibers within the lobules of the thyroid gland. See also thyroid gland.
, spermatogonia, spermatocytes, and spermatozoa spermatozoa

see spermatozoon.
 arranged in characteristic bands (Photo 2a).

Ripe Stage

In females, all follicles are filled with ripe vitellogenic oocytes of polygonal pol·y·gon  
n.
A closed plane figure bounded by three or more line segments.



po·lygo·nal adj.
 shape containing mature yolk granules Granules
Small packets of reactive chemicals stored within cells.

Mentioned in: Allergic Rhinitis, Allergies
 (Photo 1b). No empty space was observed between the follicles. In males, the ripe stage cannot he distinguished from the developing stage, and is therefore omitted.

Spawning Stage

In females, because most oocytes in the follicles are discharged into the environment, the lumen of the follicles becomes essentially empty. Spawned ovaries Ovaries
The female sex organs that make eggs and female hormones.

Mentioned in: Choriocarcinoma

ovaries (ō´v
 are characterized by the presence of spaces between the free oocytes in the lumen (Photo 1c). In males, the lumen of the follicles is partially empty with spaces inside, and a decrease in the quantity of spermatozoa can be noticed. The spermatocytes remain at the follicular fol·lic·u·lar
adj.
1. Relating to, having, or resembling a follicle or follicles.

2. Affecting or growing out of a follicle or follicles.
 walls (Photo 2b). In this stage the spermatic ducts spermatic duct
n.
See vas deferens.
 are filled with spermatozoa (Photo 2b and 2c).

Recovery Stage

In males and females, after spawning the gonads are collapsed, and each follicle follicle /fol·li·cle/ (fol´i-k'l) a sac or pouchlike depression or cavity.follic´ular

atretic ovarian follicle  an involuted ovarian follicle.
 is empty. In females few residual oocytes are present, being phagocytized by amoebocytes. The gonads are reduced to a thin layer of tissue adjoining the hepatopancreas The hepatopancreas is an organ of the digestive tract of arthropods, gastropods and fish. It provides the functions which in mammals are provided separately by the liver and pancreas.  (Photo ld). No active oogenesis is evident. In males phagocytosis phagocytosis: see endocytosis.
Phagocytosis

A mechanism by which single cells of the animal kingdom, such as smaller protozoa, engulf and carry particles into the cytoplasm.
 occurs of the residual spermatozoa by amoebocytes, and no active spermatogenesis are evident. However, not in all samples in the recovery stage are the gonads visible because they have been completely absorbed and therefore it is only possible to determine anatomically the sex of the animals by the presence or absence of a penis

Mean Maturity Index

Grant and Tyler (1983) proposed using the term "maturity index" for examinations of gonad histological sections Histological section refers to thin slices of tissue applied to a microscopic slide, usually around 5 to 10 micrometres thick, which are viewed under a microscope.

Sections are usually stained with dyes to give optical contrast before viewing.
 and restricting the use of "gonad index" to the quantitative analysis Quantitative Analysis

A security analysis that uses financial information derived from company annual reports and income statements to evaluate an investment decision.

Notes:
 of relative gonad weight or size. We obtained the mean maturity index for each monthly sample, according to the method described by Seed (1976) and Kautsky (1982) for the bivalve bivalve, aquatic mollusk of the class Pelecypoda ("hatchet-foot") or Bivalvia, with a laterally compressed body and a shell consisting of two valves, or movable pieces, hinged by an elastic ligament.  Mytilus edulis (Linne 1758). The number of animals in each stages of maturity was multiplied by the numerical ranking of the stage (recovering = 1; developing = 2; ripe = 3; spawning = 4) and by dividing the sum of these products by the number of individuals in the sample. The index varies from one, if the female gonads of the entire population are recovering and 4 if the whole female population is spawning. In the male population, because the ripe stage is missing, the index will be 3 if all animals are in the spawning stage, and 1 if all animals are recovering.

Biological Minimum Size at Sexual Maturity

To determine the minimum size at sexual maturity we selected from all collected animals the 10 smallest females and males from each location and determined their stage of gonadal maturity.

Sex Ratio of the Histologically his·tol·o·gy  
n. pl. his·tol·o·gies
1. The anatomical study of the microscopic structure of animal and plant tissues.

2. The microscopic structure of tissue.
 Examined Specimens

The total number of males and females collected at Punta Perico and Playa Cerritos was subjected to the X2 test to examine whether statistically significant differences exist between the numbers of the different sexes examined histologically.

RESULTS

Copulation copulation /cop·u·la·tion/ (kop?u-la´shun) sexual union; the transfer of the sperm from male to female; usually applied to the mating process in nonhuman animals.

cop·u·la·tion
n.
1.
, Egg Capsule Deposition, and Water Temperature

During the collection of the snails we observed at Playa Cerritos and at Punta Perico year-round copulations, whereas egg capsules could be found on both sites only during February to May. During this period at Punta Perico water temperatures of 24[degrees]C to 26[degrees]C were measured. The water temperature in summer reached up to 32[degrees]C. At Playa Cerritos slightly lower water temperatures were measured: January up to May of 19[degrees]C to 20[degrees]C, and during summer up to 28[degrees]C (Fig. 2). No relation could be determined between the water temperature and the copulation and capsule deposition.

[FIGURE 2 OMITTED]

Color of the Gonads

Marked variations in the color of the gonads could be observed during different sampling dates. During September to October the gonads were dark brown, and no sexual differences could be observed. In contrast from November until April the female gonads were yellow, whereas the male gonads were brown. The histological observation that the gonadal maturity is uniform in different parts of the gonad confirmed the uniform coloration col·or·a·tion  
n.
1. Arrangement of colors.

2. The sum of the beliefs or principles of a person, group, or institution.
 of the formol-fixed gonads.

Sex Ratio

In this 20-mo study we examined histologically 544 gonads from snails collected at Playa Cerritos (260 females, 284 males) and at Punta Perico 543 specimens (221 females, 322 males). Applying the [chi square chi square (kī),
n a nonparametric statistic used with discrete data in the form of frequency count (nominal data) or percentages or proportions that can be reduced to frequencies.
] test we examined the hypothesis that the sex ratio is 1:1. For the animals from Playa Cerritos the calculated P value was 0.3 showing that no statistically significant differences existed between the number of males and females. In contrast at Punta Perico were found statistically significant differences in the sex ratio (P < 0.001). More males than females were found.

Gonad Reproductive Cycle

Punta Perico

In gonads from female snails collected at Punta Perico the developing stage was found nearly during the whole sampling period, with the exception of September to October 2000, and October 2001. In December 2001, 90% of the nine examined female gonads were in the developing stage. Female gonads were found in the ripe stage from June to August and November 2000, and from February to June 2001 and in January 2002, with the highest percentage in June 2000 (40% from 7 animals) and in February 2001 (36% from 11 animals).

Female gonads in the spawning stage were observed from June to August 2000, January to September 2001 and in January 2002. The highest frequency of spawning occurred in August 2000 and March 2001 (41% from 12, and 60% from 10 animals, respectively). Female gonads in the recovery stage were observed during nearly the whole sampling period, with the exception of June 2000 when no gonad was found in the recovery stage. In September to October 2000 and in October 2001, 100% of the 32 samples studied were in the recovery stage (Fig. 3a).

[FIGURE 3 OMITTED]

Male gonads from snails collected at Punta Perico were in the developing stage during the whole observation period, with two peaks of 100%: one in November 2000 (12 gonads studied) and another in December 2001 (19 gonads examined).

Individuals in the spawning stage were found during two clearly defined periods, one from June to September 2000, and another one from December 2000 until June 2001. Also in January 2002 the beginning of another spawning stage was seen. One spawning peak was found in February to March 2001 with 95% from a total of 39 male gonads studied. In September 2000, 87% of the 16 male gonads were examined in the recovery stage, and in September 2001 80% from a total of 15 gonads (Fig. 3b).

Playa Cerritos

Female gonads in the developing stage could be observed during the whole sampling period, with the exception of October 2000 and October to November 2001. Two peaks occurred, one in January and another in June to July 2001. In January 2001 all 15, and in June to July 82% from the 23 examined female gonads were in the developing stage.

The ripe stage of the female gonads showed two peaks of activity: one in June 2000 with 50% (12 gonads examined) and another in April 2001 with 40% from 12 examined gonads.

The spawning stage was observed between June up until August 2000 and March up until September Until September is a 1984 romantic drama set in France. It stars Karen Allen as an American tourist in Paris who falls in love with a married Frenchman (Thierry Lhermitte). External links  2001. In August 2000 from 17 examined gonads, 47% were in the spawning stage; in March 2001 from 14 examined gonads, 71% were in the spawning stage, and in August 2001 from 17 observed gonads, 24% were in the developing stage.

The recovery stage was observed during the periods; from August to December 2000 with a peak in October (100% from 12 examined gonads), and June 2001 to January 2002 with a peak in October to November 2001 (100% from 26 examined gonads) (Fig. 3c).

The male gonads in the developing stage were observed for the whole sampling period, with the exception of September 2000 and during October 2001. Two peaks of activity were observed: in November, December 2000, and January from 38 examined male gonads were all 100%, and in December 2001 from 14 gonads 86%, in the developing stage.

Spawning took place from June to August 2000, with a peak in February 2001 (100% from 15 examined gonads), and from February to September 2001, with a peak in April 2001(85% from 14 examined gonads).

The recovering stage was mainly observed from August to October 2000, with a peak in September 2000 when all (100%) of the 10 examined gonads was in the recovering stage. In 2001 the recovering stage was observed from July to November with peaks in September (64% from 14 examined gonads) and October (100% from 19 examined gonads; Fig. 3d).

Mean Maturity Index

Insight into the reproductive cycle of P. pansa was obtained from the combination of the monthly assessments of the gonad reproductive cycle and the monthly mean maturity index.

The mean maturity index for female gonads collected at Playa Cerritos had values above 2 during January to August, with peaks in February and March, demonstrating that the majority of the snail population was in the ripe and spawning stage. In September to October the majority of the gonads are found in the recovering stage (Fig. 4b). The situation of the mean maturity index of the male gonads is very similar. From December to August the majority of the population is in the spawning stage, and from September to October the gonads are recovering.

[FIGURE 4 OMITTED]

The majority of the female gonads from snails collected at Punta Perico had during January to August a mean maturity index >2.0, demonstrating that they were, like at Playa Cerritos, in the ripe and spawning stage. An index value below 2.0, as observed from September to December, showed that they were in the recuperating stage (Fig. 4a). The same situation can be found in male gonads: the majority of the population was in the spawning stage during November to July, and only during August to October in the recovering stage. The data on the mean maturation index agreed well with the histological results described previously.

Size at Sexual Maturity

The 10 smallest female snails from the 260 females collected at Playa Cerritos had a total SL between 13.0-19.08 mm, and the size of the 10 smallest males from 284 animals SL ranged from 14.8618.56 mm. In the females the gonad development stage was up to 18.77 mm SL, either recovering or developing. Spawning could be observed in females larger than 18.84 mm. In males, spawning could only be observed in animals larger than 18.00 mm. A similar situation could be observed from the snails collected at Punta Perico. The size of the 10 smallest females from 221 animals collected ranged from 16.37-21.00 mm and the size of the 10 smallest males from 322 animals ranged from 14.8-19.6 mm. Only one female of a size of 17.3 mm showed gonad development, larger animals were in the developing, ripe, spawning, or recovering stage. The gonads of the males were either in the developing (7) or in the recovering (2) stage. One male snail with a size of 18.94 mm had a gonad with signs of having spawned.

DISCUSSION

Reproductive Cycle of P. pansa

The timing and duration of the reproductive cycle of P. pansa from gonad development through developing, ripe, spawning, and recovering is controlled by an interaction of environmental and endogenous endogenous /en·dog·e·nous/ (en-doj´e-nus) produced within or caused by factors within the organism.

en·dog·e·nous
adj.
1. Originating or produced within an organism, tissue, or cell.
 factors. Activation of the gonads is probably controlled by endocrine hormonal factors being initiated in connection with lowered water temperature. With increasing air and water temperatures gonad development is starting and rapidly leading to maturation. Such effects were noticed by Chung et al. (2002) during studies of the reproductive cycle of the Korean muricid Rapana venosa (Valenciennes 1846). Kautsky (1982) made similar observations with the bivalve Mytilus edulis. Detailed information about the reproductive cycle of P. pansa is only sparingly spar·ing  
adj.
1. Given to or marked by prudence and restraint in the use of material resources.

2. Deficient or limited in quantity, fullness, or extent.

3. Forbearing; lenient.
 available, mainly as thesis work, and it is difficult to compare one study with the other. Hernandez-Cortes and Acevedo-Garcia (1987) mention that copulation of P. pansa occurs at the Pacific coast of Oaxaca during the hot season from March until July, with the peak of occurrence in May, and from June to July the females are laying their egg capsules. Similar observations from Oaxaca are reported by Turok et al. (1988), who additionally mention that the peak of capsule deposition is in June, and that this continuous activity leads to a constant production of young animals YOUNG ANIMALS. It is a rule that the young of domestic or tame animals belong to the owner of the dam or mother, according to the maxim Partus sequitur ventrem. Dig. 6, 1, 5, 2; Inst. 2, 1, 9.  during July, up until September.

In a histological study about the gonad development of P. pansa collected in Nayarit, Quiroz-Rocha (1992) reported that during December to January the gonads are in the resting (immature) stage and that spermatozoids can be scarcely found in male gonads. During May to July the gonads are in the developing stage, and reaching the ripe stage during August to September. In a more detailed histological study about the gonad development cycle of P. pansa further north from Sinaloa, Gonzalez-Flores (1997) reported that the recovering period occurs from September to October, but can be extended up until November to December. The developing stage can be observed in January to February but possibly can be extended during the whole year.

Copulation and the ripe stage of the gonads can be observed from March until July. Spawning starts in May and lasts until July. Acevedo-Garcia et al. (1993) report, that females larger than 2 cm lay egg capsules during December up until September. In our study however, we could show that P. pansa can reproduce during the whole year with the highest frequency of spawning occurring in March and August. For adequate natural resources management of P. pansa in Baja California Sur, strict prohibitory measures should be enforced for exploiting animals during the developing, ripe, and spawning stages of the gonads, and only after special considerations should collections be permitted from September to October, when the animals are in the recovering stage.

Influence of the Water Temperature on the Reproductive Cycle

In most prosobranchs the reproductive cycle is in synchrony synchrony /syn·chro·ny/ (-krah-ne) the occurrence of two events simultaneously or with a fixed time interval between them.

atrioventricular (AV) synchrony
 throughout a population, controlled by some kind of exogenous Exogenous

Describes facts outside the control of the firm. Converse of endogenous.
 and/or endogenous controlling mechanisms (Webber 1977). Important exogenous factors for the gonad development of marine gastropods are considered to be temperature, nutrition, and photoperiod photoperiod /pho·to·pe·ri·od/ (fo´to-per?e-od) the period of time per day that an organism is exposed to daylight (or to artificial light).photoperiod´ic

pho·to·pe·ri·od
n.
 (Webber 1977, Martel et al. 1986). In temperate climates the seasonal changes of the temperature together with changes in the photoperiod are considered important factors controlling the gonad development, however in tropical zones where seasonal temperature fluctuations are less pronounced, temperature does not have such a marked impact. Many species have a seasonal spawning cycle spawn during springtime, and some even in winter (Webber 1977). In Argentine, in the southwestern Atlantic Ocean Atlantic Ocean [Lat.,=of Atlas], second largest ocean (c.31,800,000 sq mi/82,362,000 sq km; c.36,000,000 sq mi/93,240,000 sq km with marginal seas). Physical Geography
Extent and Seas
 (Mar del Plata Mar del Plata (mär thĕl plä`tä), city (1991 pop. 519,707), E central Argentina, on the Atlantic Ocean. It is one of the most popular seaside resorts in South America. Fishing and fish processing are also important industries. ), Zidonia dufresnei (Donovan 1823) spawns during spring and summer (Gimenez & Penchaszadeh 2002). In Coquimbo, North Chile, the subtidal gastropods Priene scabrum (King 1832) spawn in winter, and Sinum cymba (Menke 1828) during almost the whole year (Romero et al. 2003). At the Pacific coast of Bahia Tortugas, Baja California Sur, Mexico, the wavy turban snail Astrea undosa (Wood 1828) spawns during the whole year, with spring and autumn as the major intensive spawning seasons (Belmar-Perez et al. 1991). In Oaxaca Hernandez-Cortes and Acevedo-Garcia (1987), as well as Gonzalez-Flores (1997) observed in Sinaloa the main spawning season of P. pansa is during the summer months of May to July. In Baja California Sur P. pansa has a spawning season from January to July until August, however, mainly in February to April during relative cold, and July to August during warm water and air temperatures. The gonad reproductive cycle of P. pansa seems therefore to be correlated with the temperature. The time of spawning of P. pansa might also be correlated with periods of decreasing differences between low and high tides. A decrease in the tidal range is observed in January to March and June to July up until September. During these periods the laid egg capsules are located either a short distance under the water surface or in water-splashed areas.

Sex Ratio

Differences in the sex ratio of a mature population of gonochoristic species can be used to check whether there is differential growth or mortality rate between the two sexes (Gimin & Lee 1997). In this study we examined the gonads from 284 males and 260 females collected at Playa Cerritos and no statistically significant difference was detected in the ratio between males and females. Also in Jalisco no difference in the male to female ratio could be found (Leon-Alvarez 1989). However, at Punta Perico a significant statistical difference in the male/female ratio (1:0.74) was observed. At this location we examined the gonads from 322 males and 221 females. The difference in the male/female ratio could be explained by the different conditions of the rocky shore at Playa Cerritos and Punta Perico. At Playa Cerritos, even at high tides, all the rocks are never completely submerged the water. In contrast, at Punta Perico, during high tides a great part of the shore is totally submerged and offering only limited hiding places to the snails, which need protection against displacement by the strong impact of the waves. To avoid the displacement by strong wave actions the snails prefer protective areas where they can hold fast onto the substrate (Hernandez-Cortes & Acevedo-Garcia 1987). Because females reach larger sizes, they are more endangered to be displaced by wave actions and currents than males (Denny et al. 1985). Although the reason is not mentioned, both Hernandez-Cortes & Acevedo-Garcia (1987) and Alvarez-Diaz (1989) reported that on the Pacific coast of Michoacan, males can be found in greater numbers than females (1: 0.83) and (1:0.75), respectively. Similar results were obtained by Turok et al. (1988) (1:0.78), Hernandez-Cortes, and Acevedo-Garcia (1987) in Oaxaca; and in Jalisco by Reyes-Aguilera (1993) (1:0.84), Fonseca-Madrigal (1998) (1:0.72), and by Michel-Morfin et al. (2000) (1: 0.75). Another explanation for the occurrence of more anatomical males than females in a sample could be imposex, caused by the organic metal compound, tributyltin, which is used as a antifouling paint Noun 1. antifouling paint - a paint used to protect against the accumulation of barnacles etc. on underwater surfaces
paint, pigment - a substance used as a coating to protect or decorate a surface (especially a mixture of pigment suspended in a liquid); dries to
 in shipyards, and which is leading to erroneous classification of males and females, resulting in a higher number of males (Gooding et al. 1999, Penchaszadeh et al. 2001). The comparison of our visual anatomical inspection Of the animals with the histological examinations of the gonads show that the differences in the dominance of males at Punta Perico cannot be explained by imposex. The collection of the purple snail by fishermen as a bait and even as a specialty food could also be a reason for an unequal sex ratio. Fishermen prefer larger animals, and for this reason female snails are more sought after. In Punta Perico the population of P. pansa is not exploited by fishermen, and only environmental conditions could explain the unequal sex ratio observed there.

Minimum Size at Sexual Maturity

The determination of the minimum size at sexual maturity of any species of commercial interest is an important parameter for considerations of management and exploitation. Only fragmented results are available about the life history of P. pansa. After spawning, intracapsular development until hatching takes six to eight weeks at 22[degrees]C (Naegel et al. 2003, Naegel 2004, Naegel & Gomez del Prado-Rosas 2004). The duration for settling and metamorphosis metamorphosis (mĕt'əmôr`fəsĭs) [Gr.,=transformation], in zoology, term used to describe a form of development from egg to adult in which there is a series of distinct stages.  of the veliger ve·li·ger  
n.
A larval stage of a mollusk characterized by the presence of a velum.



[New Latin v
 larvae Larvae, in Roman religion
Larvae: see lemures.
 after spawning takes at least the same length of time (Naegel et al. 2003). The growth, environmental optimal range, and food requirements of the settled juveniles smaller than 6 mm are as yet unknown. Certainly, for a snail to reach this size after spawning more than one year is needed. In this study we show that juveniles of P. pansa do not reach sexual maturity until they reached a size of more than 18 ram. It can be concluded that the purple snails begin to spawn when they reach a size of at least 18 mm. At this size they are at least two or three years old (Ramirez-Rodriguez & Naegel 2003). This extremely slow growth and long period before reaching sexual maturity could be caused by the harsh intertidal environmental conditions, such as the risk of desiccation des·ic·ca·tion
n.
The process of being desiccated.



desic·ca
 and overheating Overheating

An economy that is growing very quickly, with the risk of high inflation.
 through several hours of daily exposure to air, sun, and current reversal during the tidal cycle. Similar observations were made with the mangrove mangrove, large tropical evergreen tree, genus Rhizophora, that grows on muddy tidal flats and along protected ocean shorelines. Mangroves are most abundant in tropical Asia, Africa, and the islands of the SW Pacific.  snail Thais kiosquiformis (Duclos 1832), which showed a growth of only ~1 mm/year, and reaches the onset of sexual maturity at a SL of ~24 mm (Koch & Wolff 1996).

In view that P. pansa is in Mexico, because of overexploitation in the past, today a species under special protection, and in view of the extremely slow growth rate, collecting snarls <18 mm can potentially cause a drastic reduction in recruitment, and for this reason should not be permitted.

ACKNOWLEDGMENTS

The authors thank Jorge Lopez- Rocha for his valuable help during the snail collections and for his excellent histological work. The authors also thank Oscar Armendariz lot drawing the figures and Chris Cooksey (London) for proof reading of the manuscript. The study was financially supported by a grant from the Conchologists of America, Inc., US-MEXUS, and by CONACYT CONACYT Consejo Nacional de Ciencia y Tecnología (National Board of Science and Technology; Mexico, Bolivia, Paraguay)  (Project 31566 N). Both authors received grants from the Instituto Politecnico Nacional (COFAA, EDI (Electronic Data Interchange) The electronic communication of business transactions, such as orders, confirmations and invoices, between organizations. Third parties provide EDI services that enable organizations with different equipment to connect. ).

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Presence of hemorrhages in the skin, often associated with bleeding from natural cavities and in tissues. Major causes include damage to small artery walls (as in vitamin deficiency or allergic reaction) and platelet deficiency (in association with such disorders as
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LUDWIG C. A. NAEGEL * AND FEDERICO A. GARCIA-DOMINGUEZ Centro Interdisciplinario de Ciencias Marinas, Instituto Politecnico Nacional Apdo. Postal 592, La Paz La Paz, city, Bolivia
La Paz (lä päs), city (1992 pop. 713,378), W Bolivia, administrative capital (since 1898) and largest city of Bolivia. The legal capital is Sucre.
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* Corresponding author. E-mail: lnaegel@ipn.mx
TABLE 1.

                                       Males

                          Avg. Total    Stand. Deviat.
Punta Perico     Number   Length (mm)   [+ or -] (mm)    Range (mm)

June 2000          11        30.28           3.92         23.9-40.7
  July             14        35.35           4.36         26.1-45.0
  August           14        30.20           5.71         19.6-45.02
  September        16        31.04           4.24        26.82-38.33
  October          19        32.17           6.49        20.88-48.93
  November         12        32.18           5.31        24.23-43.6
  December         11        33.09           5.41        25.62-47.83
January 2001       19        30.84           4.48        17.63-41
  February         19        31.73           4.56        25.11-41.01
  March            20        30.35           5.75        22.67-43.68
  April            18        29.17           5.56        20.82-47.42
  May              20        31.59           5.87         22.8-45.82
  June             20        27.51           7.37        18.76-44.03
  July             15        27.42           3.7         21.84-34.63
  August           11        29.64           6.05        22.48-45.21
  September        15        29.58           4.95        19.95-39.02
  October          12        30.12           5.57        20.83-40.36
  November         18        29.36           5.27        17.49-39.46
  December         19        30.01           4.9         20.49-40.05
January 2002       19        27.83           3.47         14.8-34.67

Total             322        30.38           5.43

                                       Females

                          Avg. Total    Stand. Deviat.
Punta Perico     Number   Length (mm)   [+ or -] (mm)    Range (mm)

June 2000           7        37.03          10.62           23-58.7
  July             14        35.71           4.26         26.0-44.2
  August           12        33.33           7.21        23.16-47.46
  September         3        36.9            4.31        32.75-42.55
  October          10        34.19           6.32         23.3-45.68
  November          8        34.18           4.73        24.75-41.55
  December         16        35.45           4.18        25.08-47.14
January 2001        9        31.25           4.40         19.2-40.03
  February         11        38.11           2.86        21.95-44.59
  March            10        33.57           4.36        21.99-42.37
  April            12        33.62           7.96        21.17-50.33
  May               9        34.87           6.58        23.36-49.22
  June             15        36.22           8.91        18.44-50.38
  July             10        33.48           5.29        16.37-45.11
  August           15        30.19           3.27        24.51-37.17
  September         9        32.88           4.77         25.9-40.53
  October          19        32.29           5.18        22.45-46.31
  November         13        27.75           4.64        19.09-36.88
  December          9        33.92           4           23.13-40.37
January 2002       10        32.24           5.72        23.06-42.11

Total             221        33.64           6.00

                          Avg. Total    Stand. Deviat.
Playa Cerritos   Number   Length (mm)   [+ or -] (mm)    Range (mm)

June 2000          11        27.53           3.39         22.3-31.1
  July             16        26.76           3.58         21.0-43.5
  August           12        29.75           2.51        25.06-32.55
  September        10        28.42           2.96        23.46-31.59
  October          17        28.54           4.25        21.62-35.66
  November         11        27.89           2.93        17.18-27.64
  December         12        23.31           3.18        17.18-27.64
January 2001       15        25.28           2.8         19.01-29.05
  February         11        26.17           4.82        19.01-29.05
  March            16        24.86           4.36        18.31-34.73
  April            14        28.05           3.91        21.25-35.38
  May              12        29.25           4.33        23.53-40.81
  June             19        26.48           3.81        20.74-32.76
  July             17        23.4            3.07        18.56-29.4
  August           14        25.58           4.7         18.34-36.44
  September        14        21.5            3.28        15.87-35.82
  October          19        23              3.8         14.86-28.4
  November         15        24.52           2.33        19.84-28.57
  December         14        24.63           2.69        18.98-29.95
January 2002       15        26.79           3.54        20.21-33.43

Total             284        25.93           4.11

                          Avg. Total    Stand. Deviat.
Playa Cerritos   Number   Length (mm)   [+ or -] (mm)    Range (mm)

June 2000          12        31.17           3.72         24.2-36.3
  July              8        27.16           5.68         20.5-40.6
  August           17        34.39           5.86        24.81-48.38
  September         9        31.37           6.78        23.89-46.55
  October          12        29.08           6.16        23.07-41.12
  November         10        29.85           5.81        24.41-42.93
  December         17        29.85           5.38        24.41-42.93
January 2001       15        29.71           5.83        21.97-44.96
  February          7        29.12           6.2          21.1-41.77
  March            14        27.51           6.69        18.84-41.71
  April            15        28.43           4.68        23.08-42.47
  May              16        29.36           2.69        23.97-33.78
  June             11        29.64           4.58        20.28-36.45
  July             12        26.54           3.57         21.7-34.17
  August           17        27.32           5.53        20.65-38.31
  September        13        25.14           5.39           13-33.42
  October          12        25.83           4.33        16.71-31.52
  November         14        28.81           7.14        15.94-41
  December         17        28.28           5.71        15.88-38.61
January 2002       12        28.78           5.04        17.74-36.89

Total             260        28.92           5.62
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Plicopurpura pansa (Gould, 1853) from the Pacific Coast of Mexico and Central America: a traditional source of Tyrian Purple.
Variations in density, shell-size and growth with shore height and wave exposure of the rocky intertidal snail, Calyptraea spirata (Forbes, 1852), in...
Reproductive biology of the "Copey" snail Melongena melongena (Linnaeus, 1758) in Cispata Bay on the Caribbean coast of Colombia.
Molluscan communities of the rocky intertidal zone at two sites with different wave action on Isla La Roqueta, Acapulco, Guerrero, Mexico.
The effect of periodically "milking" to obtain Tyrian Purple from Plicopurpura pansa (Gould, 1853) on the frequency of expulsion and mortality.
Biological and chemical properties of the secretion from the hypobranchial gland of the purple snail Plicopurpura pansa (Gould, 1853).
Reproductive cycle of the rock oyster hyotissa hyotis (Linne, 1758) (Griphaeidae) at the La Ballena Island, Gulf of California, Mexico.
The hypobranchial gland from the purple snail Plicopurpura pansa (Gould, 1853) (prosobranchia: Muricidae).
Can the collection of "Tyrian purple" from Plicopurpura pansa (Gould, 1853) (Prosobranchia, Muricidae) be blamed for its declining population?
Reproductive pattern of the squalid callista Megapitaria squalida from Northwestern Mexico.

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