Notes on reproduction of the littoral skink Emoia Atrocostata (Squamata: Scincidae) from Oceania.
A sample of 45 E. atrocostata consisting of 27 adult males, 1 5 adult females and three juveniles, deposited in the Bernice P. Bishop Museum (BPBM) Honolulu, Hawaii, USA was examined. The E. atrocostata specimens were collected in the period 1962 to 2008 from the Caroline Islands, Irian Jaya, Malaysia, Northern Mariana Islands, Papua New Guinea and Solomon Islands.
Material examined.-Malaysia Pulau Jarak, (7895, 7896, 7898); Northern Mariana Islands: Guguan (26863), Saipan (26853), Tinian (31708); Caroline Islands: Yap (34541-34544); Irian Jaya (3722); Papua New Guinea: Milne Bay Province (16706-16710, 19967, 19969-19974, 19976-19979), Madang Province (11758, 13568), Morobe Province (13568), New Ireland Province (12015), West Sepik Province (13496-13501, 13503); Solomon Islands: Western Province, Choiseul Island (12774), Ranongga Island (12827-12830), Vangunu Island (12922, 12923), Uipi Island (12982).
The left gonad was removed from each skink and embedded in paraffin. Histological sections were cut at 5[mu]m and stained by hematoxylin followed by eosin counterstain (Presnell & Schreibman 1997). Enlarged follicles > 4 mm length and oviductal eggs were counted. Histology slides were deposited in BPBM. The snout-vent length (SVL) of each specimen was measured from the tip of the snout to the posterior margin of the vent. An unpaired t-test was used to compare E atrocostata male and female mean body sizes (SVL) utilizing Instat (vers. 3.0b, Graphpad Software, San Diego, CA).
There was no significant size difference between the males (mean SVL = 72.7 mm [+ or -] 8.4 SD, range = 53-88 mm), and females (mean SVL = 67.9 mm [+ or -] 6.6 SD, range = 57-88 mm) (unpaired t-test, df = 40, t = 1.91, P = 0.063). Juveniles averaged (SVL = 49.7 mm 1.5 SD, range = 48-51 mm). The smallest reproductively active male (spermiogenesis in progress) measured 53 mm SVL (BPBM 13500) and was collected in September. Two stages were noted in the testicular cycle: (1) spermiogenesis (= sperm formation), in which the seminiferous tubules were lined by clusters of sperm or clusters of metamorphosing spermatids; and (2) regressed, in which the seminiferous tubules were reduced in size and contain mainly spermatogonia and interspersed Sertoli cells. All males > 53 mm were undergoing spermiogenesis. These were by month: January: Papua New Guinea (n = 3); February: Solomon Islands (n = 4); March: Solomon Islands (n = 1); April: Papua New Guinea (n = 7), June: Northern Marianas 1, Malaysia 2 (n = 3); July: Caroline Islands 1, Northern Marianas 1 (n = 2); August: Caroline Islands, 1, Irian Jaya 1, Papua New Guinea, 1, (n = 3); September: Papua New Guinea (n = 3). One male from July (BPBM 7898) measured 48 mm SVL and contained a testis with regressed seminiferous tubules, so it was considered to be a juvenile.
Four stages were present in the ovarian cycle (Table 1): (1) quiescent, no yolk deposition present; (2) early yolk deposition, with basophilic yolk granules in the ooplasm; (3) enlarged ovarian follicles > 4 mm diameter; (4) oviductal eggs present in the oviducts. The smallest reproductively active females (2 follicles > 4 mm) each measured 64 mm SVL. They were (BPBM 13499), which was collected in September and (BPBM 31708), which was collected in July. One female from West Sepik Province, Papua New Guinea from September (BPBM 13499) contained enlarged follicles > 4 mm and was undergoing concurrent yolk deposition in a smaller follicle for a subsequent clutch, indicating E. atrocostata can produce multiple clutches in the same year. Nine females contained an invariant clutch size of 2.0 eggs. Two smaller females (BPBM 34543, SVL = 51 mm; BPBM 19967, SVL = 50 mm) contained quiescent ovaries and were considered as juveniles.
Table 1. Monthly stages in the ovarian cycle of 15 Etnoia atrocostata. * One female from September with enlarged follicles > 4 mm was undergoing concurrent yolk deposition in a smaller follicle for a subsequent clutch. Emoia atrocostata were from: C = Caroline Islands, NM = Northern Marianas, PNG = Papua New Guinea, S - Solomon Islands. Month N Quiescent Early yolk Enlarged follicles Oviductal deposition >4 mm Eggs January 3 1 (PNG) 1 (PNG) 1 (PNG) 0 February 1 1 (S) 0 0 0 March 2 0 0 US) 1 (S) April 3 1 (S) 0 1 (S) 1 (S) May 1 0 0 0 1 (PNG) July 2 0 0 1(NM) 1(C) September 3 2 (PNG) 0 1 *(PNG) 0
An extended reproductive cycle was reported for E. atrocostata by Auffenberg & Auffenberg (1989) in the Philippines, where the prolonged reproduction of E. atrocostata may be feasible because of the continuously warm, relatively aseasonal habitat occupied by this littoral species. Auffenberg & Auffenberg (1989) concluded sperm production in E. atrocostata in the Philippines was spread evenly through most of the year but did not record a minimum size of maturity in males.
Auffenberg & Auffenberg (1989) reported that the smallest mature female E. atrocostata from the Philippines measured 71 mm SVL. During this study, one female from West Sepik Province, Papua New Guinea (BPBM 13499) and one female from Tinian Island, Northern Marianas (BPBM 31708) were found that were mature at 64 mm SVL, indicating females mature at a larger minimum size in the Philippines. An extended period of egg production was reported in the Philippines, as young were produced continuously during the year (Auffenberg & Auffenberg 1989). Emoia atrocostata produced small clutches of 1-3, usually two eggs, in the Philippines and no evidence of multiple clutches was reported, although it was believed to be possible (Auffenberg & Auffenberg 1989). Herein is provided histological evidence that multiple clutches likely are produced by E. atrocostata.
Information on reproduction in other species of Emoia skinks from Oceania reveals prolonged reproductive cycles and small clutch sizes of predominately two eggs (Baker 1947; Schwaner 1980; McCoy 2006; Goldberg & Kraus 2008) and the production of multiple clutches also appears frequently (Goldberg & Kraus 2008). An exception is Emoia sanfordi, endemic to the Vanuatu Archipelago, which produces clutches of 2-7 eggs (Hamilton et al. 2008).
While reproductive activity was exhibited (by either males, females or both) of E. atrocostata in all months sampled, (January to September), larger monthly samples from different parts of its range will be needed to ascertain geographic variations in its reproductive cycle.
We thank Kathleen Imada (BPBM) for facilitating our examination of E. atrocostata. This is contribution 2011-003 from the Pacific Biological Survey at the Bishop Museum.
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SRG at: firstname.lastname@example.org
Stephen R. Goldberg and Fred Kraus
Whittier College. Department of Biology. P. 0. Box 634 Whinier, Califiwnia 90608 and Bernice P. Bishop Aluseum. Department of Natural Sciences 1525 Bernice Street. Honolulu. Hawaii 96817
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|Author:||Goldberg, Stephen R.; Kraus, Fred|
|Publication:||The Texas Journal of Science|
|Date:||Nov 1, 2010|
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