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Phenotypic plasticity in reproductive traits of Helix aperta snails sampled during or after aestivation.

INTRODUCTION

Snail farming (heliciculture) is currently attracting both scientists and farmers [31] either in food security and economic context or as a means of conserving this resource and maintaining biodiversity [1]. The achievement of such a practice in a simpler and profitable way requires a good mastery of many aspects of snails' biology, ecology, life history, genetics, nutritional needs and general husbandry. So that, many studies exploring life cycles and factors regulating activities were carried out on some edible land snails [20].

Animals in general; being in their natural habitats; are faced to fluctuations in environmental conditions including temperature, humidity and vegetation [27]. When those conditions become harsh, many species tend to exhibit morphological, behavioral, physiological and biochemical adaptations, in order to ensure their self preservation [41]. Hibernation, diapauses and aestivation constitute three important adaptive responses adopted by many organisms to escape deteriorating environmental conditions.

Snails; as many other ectotherms; lack physiological thermal control [29]. Therefore, during dry and hot spells, they withdraw into their shells, conserve water by sealing their shell aperture with a calcareous epiphragms and reduce their mobility, reproduction and growth [1]. This inactive state is known as "aestivation". It is a naturally programmed phenomenon [33,34] adopted by snails and many other animals to escape the long dry seasons that are incompatible with their active lives. Therefore, snails living under Mediterranean climates, characterized by dry and hot summers, prepare themselves as early as May to undergo a long aestivation that is essential to their survival.

Aestivation was the target of many studies, hence lots of aspects of its physiology and biochemistry were elucidated, notably for the animal groups-anuran amphibians and pulmonate land snails [42]. Primary concerns for estivators include mechanisms to conserve energy, retain body water, ration use of stored fuels, deal with nitrogenous end products, and stabilize organs, cells and macromolecules of over many weeks or months of dormancy [41]. Aestivation may be considered as a seasonally obligate event and according to Omoyakhi and Osinowo [30] it can be classified as an important phase of the snail's life cycle. Although aestivation is generally accompanied by a decrease in animal's liveweight [1,32] it is always thought to be followed by a compensatory recovery and many benefits ranging from agility, fertility, guts clearance, healing and rejuvenation [30]. However, this phenomenon has been almost completely removed from captive breeding of snails [31]; mainly because reduced production and profit and the delay in the whole breeding process. However, this may constitute a long-term serious setback for the heliciculture practice [31].

Helix aperta Born (1778) (= Cantareus apertus Born, 1778) is one edible land snail that appears among the recommended species for snail farming [9]. It originates from the Mediterranean basin and reported to occur in the south of France, Italy, Turkey, Cyprus and North Africa [21,39]. This species is heavily exploited for gastronomy and its meat highly prized. However, there is little information about it to support its farming. The land snail H. aperta is also known as the "burrowing snail". It comes up above the ground only during rainy weather; during dry conditions, it burrows 7-15 cm deep into the ground and aestivates until rain softens the soil.

To explore the importance of aestivation for this species, the present study seeks to determine the consequences of interruption of aestivation on the reproductive performances of H. aperta snails.

Material:

This study was performed on two groups of adult healthy snails Helix aperta of roughly the mean weight (see table 1, row 1). Both groups were sampled from the same place in Bakaro 22 km east of Bejaia in the Kabylie region (Northeastern Algeria; Latitude: 36[degrees].65'46.49"N Longitude: 5[degrees].19'13.83"E); in order to ensure genetic similarity between the two samples.

The first group, consisting of individuals picked up from their natural habitat on the third week of June 2011. In this period of the year, the subjects being in full aestivation, hidden under the ground with thick whitish epiphragms sealing the aperture of their shells. The snails were dug out of the soil using a small pick. For the second group, individuals were left to accomplish their aestivation and were then collected in autumn, during the 4th week of October 2011 right after their waking up.

For convenience, the snails collected during and after aestivation are coded, respectively, DE and AE samples.

Experimental procedure:

Each experiment was conducted in the laboratory immediately after collection. Snails in aestivation were first activated by spraying with luke-warm water until they emerged from their shells.

In this study, the "soilless" breeding technique was adopted. It is developed by Daguzan [11] and used by many others [12,23,14]. It is also effective in raising the helicid snail, Cornu aspersum, an ubiquitous species living beside H. aperta in Algeria.

Before setting to reproduction, all collected snails were individually weighted. In order to assess the weight variation during the experiments, the final weight was also determined at the end. Before any weighing, each snail had been cleaned to remove any stuck excrements or food possible to falsify the results. Thereafter, snails were tagged with adhesive labels to be recognized, and housed in 9x20x20 cm transparent polythene containers with a density of 15 individuals per container. Such values are also optimal for breeding activity of C. aspersum [11].

The containers had perforated lids to provide ventilation, and their bottoms lined with wet absorbent paper to maintain humidity. The breeding experiments were conducted under controlled conditions (20 [degrees]C, long- photoperiod 16 h Light: 8 h dark, 90 [+ or -] 5% RH), demonstrated optimal for breeding activity of Helix aperta snails [43,44]. The temperature was controlled by means of 12,000 BTU air conditioners (Samha, Setif, Algeria) and the light provided by daylight neon with an intensity of 50-100 lux. The neons were connected to an electronic chronometer clock set to automatically control the photoperiods.

Throughout the experiments, snails were fed with the commercial product "Helixal" (Etablissements Chays, France) developed by Gomot-de Vaufleury [18]. It is a special meal for snails whose components are reported in Gomot-de Vaufleury [18]. 50 g of this food was provided on Petri dishes of 9 cm diameter deposited in the bottom of each container. Three times a week, at the same time, the food was renewed, the containers cleaned and the absorbent paper replaced. The position of boxes was changed every day in the rearing room. Pots of 10cm diameter and 8cm height filled with wet light soil were placed in each container for egg-laying. They were replaced as soon as used.

To examine the reproduction activity, the experimental snails were observed daily throughout the experiments. At the moment of supplying with water and feed, snails were not disturbed if mating or ovipositing. All copulations and egg-layings were recorded. For this, two observations a day were made; one early in the morning, one other in the afternoon. Each laid clutch was picked up and identified by its parentage, laying and hatching dates. The laid eggs for each group were collected using a teaspoon and counted. Thereafter a number of 30 to 40 randomly chosen eggs were individually weighted with an accuracy of 0.001 g. All the eggs were then incubated in 9cm diameter/1.5cm height Petri dishes at a temperature of 20[degrees]C. To maintain humidity during the time of incubation, the Petri dishes were lined with wet absorbent paper. For aeration of the eggs, small holes of 1mm diameter each were made in the Petri dishes' lids. For each clutch, the incubation time and the hatching rate were recorded. Hatching rate could be used as a direct evaluation of the hatching success. For each group, the length of the reproduction period was estimated by measuring the time between the beginning of matings and the end of egg-laying. Death was also considered in this study. Every week and during all the time of the experiments, the number of dead animals was monitored in each group. After the last clutch, the snails were kept under observation for 5 weeks during which no mating occurred but rather inactivity and mortality drastically increased.

Statistical analyses:

Statistical analyses were carried out using the XLSTAT (2009) program. The mean weight of snails of the two groups and the mean number of eggs per clutch were expressed as means [+ or -] standard deviation (M [+ or -] SD). Student (t) test was used to compare the mean weight of snails in the two groups, the mean weight of snails within each group at the start and the end of reproduction, mean numbers of eggs per clutch as well as the mean egg weights per clutch. The chi-square (yl) test was performed to verify the association between the numbers of matings and numbers of egg layings per snail between the two groups. To estimate the relationship between weight of snails and that of the eggs, each snail' weight and its number of layings, eggs weight and clutch size as well as the hatching success in the two groups, we used the Pearson correlation test.

Results:

Snails that completed their aestivation period (AE sample) were clearly the most active sexually. Their reproductive activity lasted 7 weeks with a total of 34 recorded copulations and 39 produced clutches (see fig. 1 & table 1, rows 6 & 8). As for the DE sample, consisting of snails for which aestivation was interrupted, the reproduction activity was drastically lower. It lasted merely 4 weeks with only 13 recorded copulations and 4 produced clutches (see fig. 1 & table 1, rows 6 & 8).

Trends of the evolution of mating activities were very different for the two experimental groups. Snails from the AE sample started to reproduce earlier than their conspecifics in the DE sample. The former began the mating activity on the first week after setting to reproduction and continued up until the fifth week. By contrast, snails from the DE sample did not start to mate until the third week after setting the reproduction and continued up until the sixth week (fig. 1).

In total, mating activity lasted 5 weeks in the AE sample versus 3 weeks in the DE sample (table 1, row 16).

The peak of mating activity was observed on the third week in the first sample with 38.23% of the copulations recorded in that week. In the DE sample the peak of mating activity, corresponding to 46.15% of the total matings, was observed in the fifth week (fig. 1).

The total number of mated individuals varied significantly (P<0.05) between the two samples. In fact, the AE sample showed 100% of mating snails, while only 23.36% snails from the DE group have mated (table 1, row 5).

[FIGURE 1 OMITTED]
Descriptive traits      AE Sample Adult         DE Sample Adult
                        snails collected        snails collected
                        after aestivation       during aestivation
                        from Bejaia (North      from Bejaia (North
                        Eastern Algeria) (1)    Eastern Algeria) (1)

1. Mean weights         14.53 [+ or -] 0.76cB   13,43 [+ or -] 1.07bB
[+ or -] SD of snails
at start of
reproduction period
(g)
2. Mean weights         13.22 [+ or -] 0.85cA   12.35 [+ or -] 1.01bA
[+ or -] SD of snails
at the end of
reproduction period
(g)

3. Sample size at       23a                     23a
start of reproduction
period

4. Sample size at the   17a                     09a
end of reproduction
period

5.Percent of snails     100 %c                  23.36 %b
that mated

6. Total number of      34d                     13b
matings

7. Percent of snails    100 %d                  13.34 %b
that laid eggs

8. Total number of      39c                     4b
clutches

9. Mean number of       328.4 [+ or -] 21b      206.0 [+ or -] 32a
eggs [+ or -] SD
clutch-1

10. Mean egg weight     16.4 [+ or -] 1.09a     18.11 [+ or -] 0.32b
(mg)

11. % of hatching (=    86 %b                   68 %a
number of eggs that
gave juveniles)

12. Time between        20                      20
mating and egg-laying
(days)

13. Time of             13                      13
incubation (days)

14. Rate of mortality   26.09 %a                60.87%a
during reproduction
period (%)

15. Range of            7                       4
reproduction activity
(weeks)

16. Range of mating     5                       3
activity (weeks)

17. Range of laying     3                       2
activity (weeks)

18. Mortality rate      26.09                   60.87
during reproduction
period (%)


Table 1: compared reproductive activities of Helix aperta snails collected during and after aestivation. DE sample was collected at Bakaro/Bejaia during the third week of June 2011 (after one month of aestivation). AE sample was collected from the same place (Bakaro/Bejaia) during the fourth week of October 2011 (soon after arousal from aestivation). For some lines, the small letters next to values compare the two samples. Values with the same small letters are not significantly different (P>0.05). The capital letters compare the mean weights of snails of the two groups before and after reproduction. Values with the same capital letters are not significantly different (P>0.05).

The distribution of snails according to their total number of matings was also variable within and between the two samples. The number ranged from 1 to 4 copulations per snail in the AE sample and from 0 to 2 in the DE sample (fig. 2). The modal values of matings numbers and the corresponding frequencies were 0 (0%), 1 (13.04%), 2(13.04%), 3(39.13%), 4(34.78%) and 0(39.13%), 1(8.69%), 2(52.17%), 3(0%), 4(0%) respectively for AE and DE samples (fig. 2).

[FIGURE 2 OMITTED]

The oviposition period was expressed nearly 20 days after mating in both experimental groups (table 1, row 12). Nevertheless, a further variation was detected between the two samples in terms of egg laying activity. The laying activity was extended over a period of 4 weeks in the AE sample and over 2 weeks only in the DE sample (see fig. 3 and table 1). Egg laying frequency was also variable. Whereas 100% of mated snails from the AE sample laid eggs, only 13.34% of mated snails from the DE sample did (table 1, row 7).

[FIGURE 3 OMITTED]

Furthermore, multiple oviposition per snail was seen to occur mostly among snails from the AE sample. Effectively, in this sample a number of 1 to 3 clutches were laid per snail, while no more than one clutch per snail was produced in the DE sample. The modal values of laying numbers and their frequencies were 0(8.69%), 1(26.08%), 2(52.17%), 3(13.04%), 4(0%) and 0(82.61%), 1(17.39%), 2(0%), 3(0%), 4(0%) respectively for the AE and DE samples (fig. 4).

[FIGURE 4 OMITTED]

On the other hand, the snails with more frequent egg-layings were the ones that mated the most. Indeed, there was a highly significant association between the number of matings and egg layings per snail (P<0.001).

Likewise, the comparison of the number of eggs deposited per clutch showed that the differences between the two samples were in accordance with the previous comparison of clutch numbers. In fact, snails from the AE sample deposited the highest number of clutches with on average 328.4 [+ or -] 21 eggs per clutch. Whereas the snails from DE sample, deposited the lowest number of clutches with on average 206.0 [+ or -] 32 eggs per clutch (table 1, row 9).

No significant correlation was found between the weight of the snails and that of the eggs in both samples (R=0.191-0.267; P=0.809-0.733). Similarly, the results showed no influence of body weight and the number of layings in both groups (R=0.388-0.377; P=0.342-0.357).

Variation in clutch size, number of eggs and hatching success were largest in the AE sample snails. By contrast, variation in investment per egg; translated by the differences in eggs weight; was smallest in AE sample snails.

Indeed, significant difference in the weight of the eggs was detected between the two samples (t=3.101, P=0.02). It seemed that the snails from the DE sample were the ones to lay the heaviest eggs and snails from the AE sample the lightest ones. On average, the mean egg weight was 16.4 [+ or -] 1.09 mg and 18.11 [+ or -] 0.32 mg respectively for AE and DE sample (table 1, row 10).

A trade-off existed between clutch size and egg weight (R=-8.71, P=0.005). While the snails from the AE group invested more in larger clutches with approximately light eggs, their conspecifics from the DE group produced heavier eggs in smaller clutches.

The time of incubation period was exactly the same for both samples (13 days) but not the hatching success of eggs which was significantly different (t=4.379, P<0.0001). Snails from AE sample showed the highest hatching success (86 %); snails from the DE sample the lowest (68%) (table 1, row 11).

The degree of egg cannibalism calculated as the difference of the hatching rate to 100%; since no dead eggs were recorded; was practically higher in the DE sample (32%) than in the AE sample (14%).

Rate of mortality was very different between the two samples. During the whole experiment, 26.09 % of mortality was recorded among snails of the AE sample after intense reproductive activity. Whereas in the DE sample the percentage of mortality rose to 60.87% despite the very few clutches produced (table 1, row 18).

Weight loss during the whole experiment, calculated by subtracting the mean final weight from the mean initial one, was low and almost equal in both samples (on average 9.02% in the AE sample and 8.04% in the DE sample) (table 1, see rows 1 & 2).

Discussion:

From the results of this study, Interruption of aestivation had a negative effect on the reproduction activity of the land snail Helix aperta. According to Tafoughalt-Benbellil et al. [43], H. aperta aestivates preferentially from early May to late September in summer where temperatures are so high and did not fit the optima of this species (7-27[degrees]). Namely, the optimal aestivation duration of Helix aperta is almost 6 months. So, approximately, DE and AE samples were collected 1,5 and 6 months after aestivation respectively.

Snails collected during aestivation and allowed to reproduce right after arousal, showed a delay in the reproductive activity. They did not begin mating until the 4th week and egg-laying until the 6th week.

Whereas snails collected after aestivation (that accomplished their aestivation period) are characterized by the precocity of their reproductive activity. Indeed, they began mating right after setting to reproduction (since the first week) and the first clutch was observed in the 4th week.

Therefore it appears that aestivation is an important phenomenon in the reproduction of the H. aperta and its duration seems to influence time of mating and egg-laying activities in this species.

These observations correspond to those reported by Bonnefoy-Claudet and Deray [7] in a study performed on C. aspersum, assessing the effect of hibernation on reproductive performances of this species. In that study, Individuals C. aspersum subjected to various lengths of hibernation showed effectively different mating and laying timings. For instance, after a lengthy hibernation of about one year or more, mating occurred right after waking and the first clutch was observed in the 3d week; Whereas a delay in response to these two phenomena was observed after a month and half only of hibernation (of the order of 7 weeks for matings and 12 weeks for egg-layings) [7].

Moreover, our records on snails collected after aestivation compared favorably with those pointed out by Tafoughalt-Benbellil et al. [43]. Indeed, the authors noticed that H. aperta snails sampled on September (namely after 4 months of aestivation), mated on the first week and laid eggs on the 3-4 week. They also noticed the same behavior in snails collected approximately after two and three months of hibernation.

However, our findings are contrary to those reported by Omoyakhi and Osinowo [31]. Indeed, the authors reported an aestivation retarding effect on laying activity in the two giant African land snails Archachatina marginata and achatina achatina. For non aestivated Archachatina marginata, egg-laying took place 15 days only after pairing; whereas 72 days were needed for that after 6 weeks of aestivation. Similarly for Achatina achatina, egg-laying occurred after 13 days for non-eastivated snails and after 86 days for snails aestivated during 6 weeks. This led the authors to suggest that after aestivation, a length of time may be needed for the physiological recovery of the reproductive organs.

In our case, the short response time to copulation and egg-laying phenomena noticed in snails that accomplished their aestivation, may reflect in fact a very advanced spermatogenesis. By following the reasoning of Bonnefoy-Claudet and Deray [7], the spermatogenesis may have taken place during aestivation. Indeed, snails started reproduction immediately after aestivation, knowing that; in normal conditions; 30 to 32 days at least are needed for a spermatogenesis cycle [7].

On the other hand, the delay in response to the two phenomena quoted above (copulation and egg-laying) when aestivation is interrupted, maybe due to the inactivity of the hermaphroditic gland. As assumed by Bonnefoy-Claudet and Deray [7], this later seems to undergo a refractory period preventing it to perform its function.

In the present study; despite the same reproductive conditions provided for both samples; snails collected after a month only of aestivation showed clearly a lower reproductive effort comparing to those collected after five months of aestivation. This is illustrated by the drastic differences observed in reproductive activity length; the number of matings as well as the number of produced clutches between the two samples (see table 1, lines 15, 6 & 8).

To note, it appears clearly, that an aestivation of about 6 months is very favorable for reproduction of Helix aperta, whereas a too short aestivation period (approximately 1,5 month) is unfavorable.

Likewise, some authors have reported the same effect of hibernation which is another form of dormancy. Quoting for instance [11, 7] who underlined the necessity, in C. aspersum snails, of an hibernation period from October to March to assure a correct reproduction.

In our case, no discrepancies may be attributed neither to genetic differences (since the two samples were provided from the same region) nor to the breeding conditions which were similar and optimal in both samples.

The synchronization of the breeding experiment on snails collected after aestivation with their favorite reproductive timing could be behind their successful reproduction. The breeding experiment was performed right after sampling which took place on the fourth week of October. Effectively, Tafoughalt-Benbellil et al. [43] remarked the tendency of individuals H. aperta to copulate from early October till mid-December. The same observations were reported by Giusti and Andreini, [13] on snails H. aperta collected from Siena (Tuscany, Italy) and kept for 3 years under controlled conditions imitating those in the field. Similar behavior was also expressed by Thebapisana in Italy [13] as well as Thebapisana and Cernuella virgata in Australia [2].

However, the most convenient explanation is probably in relation with aestivation phenomenon. It seems that this later has potential benefits which improve reproduction of H. aperta snails. Obviously, arousal from "resting" or "sleeping" corresponding to aestivation, may lead to rejuvenation that enhances productivity [31].

Positive correlation was found between the number of matings and layings (R=0.791, P=0.019). This means that snails with the highest laying activity were the ones that mated more. Similar observation has also been reported by [43,44] on snails H. aperta, by [3,4] on Arianta arbustorum and by [25,26] on C. aspersum.

In both samples, laying activity started approximately 20 days after mating. This corresponds to the records of Tafoughalt-Benbellil et al. [43] on the same species hibernated for different durations then reproduced under different light and temperature regimes.

The two samples were very different in terms of laying frequency. While 100% of snails that accomplished their optimal aestivation period laid eggs, only 13.34% did among the ones for which aestivation was interrupted. Furthermore, these laters laid far less clutches comparing to the formers (4 clutches versus 39). This is Contrary to the findings of Omoyakhi and Osinowo [31] on the two giant African land snails Archachatina marginata and Achatina achatina. The authors reported a reduction in the number of clutches produced by both the two species with the length of aestivation. However, our results are in full agreement with the ones found by Bonnefoy-Claudet and Deray [7] on Cornu aspersum snails.

As pointed out by Tafoughalt-Benbellil et al. [43], this may be related to some aspects of the gonad physiology. Cytological activities of the ovotestis; including both gametic multiplication and differentiation; are strongly depending on temperature [17,16] and photoperiod [15]. It seemed that meteorological conditions during aestivation stimulate those activities. Hence, the longer the aestivation length, the more advanced gonadal activity and the more stimulated gametogenesis.

Both average clutch size and average clutch weight were significantly different between the two samples and improved by lengthy aestivation. These observations compared favourably with those reported by Omoyakhi and Osinowo [43] on Archachatina marginata and Achatina achatina snails aestivated for divergent periods.

Bonnefoy and Deray [7] assumed that during hibernation; involve physiological modifications thought to have repercussions on the reproductive activity of the snails.

It seems that such modifications involve even during aestivation. This may explain in part the mediocre reproductive activity, (in our case) upon interruption of aestivation and the eminent one when accomplishing aestivation.

Interestingly, snails collected after aestivation, adopted the "many-small eggs strategy" and the ones collected during aestivation the "few-large eggs strategy" [28]. In C. aspersum, similar behavior was seen to occur in respect to seasonal time constraints, and the two quoted reproductive strategies were adopted respectively after hibernation and after maturity [28]. Similar trend was also seen to occur among other Mediterranean species such as Helix lucorum [40], Helix texta [19] and Helix apsersa maxima [26]. Indeed, in spring those species tend to reduce their eggs number per clutch (70-80 eggs/clutch), but compensate it by increasing the weight of the eggs. Despite the greater investment of energy for the mother when producing large eggs [22]; this should be beneficial for the hatchlings. Obviously, heavier eggs have higher nutritive contains [5] leading to larger and more resistant youthful. This should allow them a better survival during the long aestivations undergone under the Mediterranean climate. Even in Western Europe, several authors have reported a reduction in eggs number per clutch with an increase in their weight during the autumnal season [45,37,35,36,8,10,25,26]. It is probably for the survival of youthful during the cold winters, which is critical for helicid populations in those regions. On the other hand, maximizing eggs numbers should increase the hatchlings numbers thus the reproductive success.

The incubation period was about 13 days for both samples. This compared favorably with the records of Tafoughalt-Benbellil et al. [43,44] on individuals H. aperta collected at different times of the year.

The percentage hatchability of the eggs was significantly different between the two samples. The least percentage (68%) occurred in snails awake from aestivation and the highest (86%) in those that accomplished their aestivation period. By taking as reference the records of Tafoughalt-Benbellil et al. [44] from snails H. aperta subjected to different combinations of temperature and photoperiod (where hatching success was of about 86% in all groups); we may assume that interruption of aestivation had negative effects on eggs hatchability. This corresponds to the deduction of Omoyakhi and Osinowo [31] that aestivation enhances hatchability in the two giant African snails Archachatina marginata and Achatina achatina.

After reproduction, low but no significant decline was detected in the mean weight of snails in both samples. For snails that aestivated for only one month, potential cause of the stability in weight may be the non exhaustion of the stored reserves, due to a short aestivation period in part; and the mediocre reproduction in another part. As for snails that aestivated longer, this stability in weight; although the intense reproduction; may be attributed to an aggressive recovery when food and water became available as pointed out by Rizzatti and Romeo [38].

In our case, it is impossible to assess weight variation due to aestivation since we could not record snails' weight before aestivation.

However, some previous studies determined the effect of aestivation duration on some land snails liveweight. Omoyakhi and Osinowo [31] reported no significant difference in the mean liveweight of the two species Archachatina marginata and Achatina chatina after being subjected to various lengths of aestivation. However, length of aestivation is generally connected to snail weight; in a way that the shorter the aestivation period, the longer the feeding period and the larger, therefore, the body size; as suggested by Cobbinah [9].

On the other hand, Abdussamad et al. [1] in their investigations on the Giant African land snail Archachatina marginata, noticed a significant decline by 35,6% at the end of 6 weeks aestivation; whereas an increase of about 57,7% by the end of 6 weeks post-aestivation. In his part, for the same species (Archachatina marginata), Omoyakhi [32] reported a weight decline of 52,4% after six weeks of aestivation, while Lukong and Onwubiko [24] reported loss of 44,6% in body weight after an aestivation of 4 months in Achatina chatina. The decrease in total body weight during dormancy was always attributed to dehydration and/or the use of energy provided by the animal's own tissues [1].

At the end of the experiments, a considerable mortality rate was recorded, despite the adequate rearing regime used that excluded several mortality factors. 26.09% of mortality occurred among snails that accomplished their aestivation period, after an intense reproductive activity. While a very high mortality was recorded (60.87%) among snails for which aestivation was interrupted.

This is contrary to the findings of Abdussamad et al. [1] who reported low and similar trend in mortality between aestivated and post-aestivated snails Archachatina marginata. However, they noticed a greater mortality in larger snails than in smaller ones, but irrespective to aestivation duration.

From the results of this study, it can be concluded that aestivation is an important phenomenon for the snails Helix aperta. Furthermore, an aestivation of about 6 months seems to be indispensable to assure a good reproduction in those snails. However, longer studies with varying lengths of aestivation could better clarify this issue.

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Meriem ABDELLI and Saida BENBELLIL-TAFOUGHALT

Laboratory of Ecology and Environment, Faculty of Nature and Life Sciences, University A. Mira of Bejaia, 06000 Bejaia, Algeria.

Address For Correspondence:

Subha.S, Assistant Professor, KLN College of Engineering, Sivagangai District, Pottapalayam, Tamil Nadu,India - 630612.

E-mail: subavarshini1308@gmail.com Phone:+91-9578848832.

Received 22 June 2016; Accepted 28 August 2016; Available online 31 August 2016
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