REPRODUCTIVE BIOLOGY OF THE AQUATIC SALAMANDER AMPHIUMA TRIDACTYLUM IN LOUISIANA

-The timing of reproductive activities in Amphiuma tridactylum is described. The vitellogenic process takes almost a full year and female reproduction is biennial or less frequent; only 35% of females were gravid. Clutch size averaged 201, ranging from 44-282, and was significantly related to body size. The relationship between body size and fat body weight was marginally insignificant. The relationship between fat body weight and clutch size was insignificant, although oocyte production significantly reduced fat body weight ournal of Herpetology, Vol. 33, No 1, pp. 10005, 1999 opyright 1999 Socety for the Study of Amphibians and Rept les eproductive Biology of the Aquatic Salamander phiuma tridactylum in Louisiana LIF ORD L. FONTE OT, JR. epartment of Biolog cal Sc ences, South astern Louisiana Unizvrsity, H mmond, Louisiana 70402, USA. Amphiuma tridactylum is a large, nocturnal, aquatic salamander that inhabits ditches, ponds, and swamps of the southeastern United States (Dundee and Rossman, 1989). It spends most of its time in burrows, from which it emerges at night to forage primarily for crayfish, although a wide variety of invertebrates, vertebrates, and carrion are eaten (Chaney, 1951; Fontenot and Fontenot, 1989). Its reproductive biology is poorly understood, being primarily based on studies from Orleans Parish (Cagle, 1948), Orleans and adjacent Jefferson parishes, Louisiana (Rose, 1966, 1967), and numerous anecdotal observations. Salthe (1973) and Sever et al. (1996) noted that some reports were contradictory, which makes interpretation of reproductive events difficult. A summary of A. tridactylum reproductive activities is as follows (but see Sever et al. [1996] for a more detailed tabulation of literature on reproductive events for Amphiuma). Wilson (1941, 1942) and Cagle (1948) suggested that female reproduction is biennial. Vitellogenesis progresses slowly at least from September through May (Wilson, 1940; Cagle, 1948; Rose, 1967). Peak sperm production occurs from December through March (Wilson, 1940; Rose, 1967). Females with sperm in their cloacae have been collected during this period, suggesting that mating occurs then (Cagle, 1948; Sever et al., 1996). Sperm are retained in female spermathecae for up to seven months until fertilization (Kreeger, 1942), and Sever et al. (1996) reported degradation of sperm in August samples from female cloacae. The nest is attended by an adult (presumably female); although the exact duration of incubation is unknown, it is probably about five months in southern Louisiana 100 This content downloaded from 207.46.13.180 on Thu, 08 Sep 2016 05:32:59 UTC All use subject to http://about.jstor.org/terms AMPHIUMA TRIDACTYLUM REPRODUCTION (Salthe, 1973). Hatching perhaps occurs sometime in the fall (Cagle, 1948; Baker, 1962). This paper provides additional data on the reproductive biology of A. tridactylum, particularly details on vitellogenesis, and synthesizes a plausible reproductive phenology for southern Louisiana. MATERIALS AND METHODS I collected a total of 146 Amphiuma tridactylum (77 males, 55 females, 14 juveniles) from Acadia and Evangeline parishes, Louisiana, from January through December, 1989. These were captured primarily at night using a variety of techniques including baited cylindrical funnel traps (85 x 25 cm; 6.4 mm mesh hardware cloth), seining, hook and line, electro-shocking, burrow excavation, artificial shelters, and hand collecting. To ensure access to aerial respiration for captured salamanders, a portion of the trap was kept above the water surface by collecting primarily at the edges of narrow ditches (0.5-2.0 m wide), swamps, and ponds. Most ditches surrounded rice, soybean, and crayfish farms and averaged about 0.5 m in depth, and were subject to drought and flooding. Occasionally, some ditches were completely dry (especially JulyOctober) and sampling was often restricted to excavating burrows in dried ditches or trapping in permanent ponds. Aquatic vegetation in both temporary and permanent water sites was predominantly alligatorweed (Alternanthera philoxeroides). The sex of each adult was determined by inspection of the cloacal walls; brown = female, light gray or pink = male (Kreeger, 1942). Dissection later showed this technique to be 100% accurate; however, some of the largest males had cloacal walls that were partially pigmented near the caudal end, but none was completely pigmented. Cagle (1948) reported the minimum adult size as 33 cm total length (TL); I used 27 cm snout-vent length (SVL) as the minimum adult size (TL = 33 cm) because of potential variation in tail length due to damaged tails (Seigel and Ford, 1988). Each individual was injected with T-61 euthanasia solution, weighed to the nearest 0.1 g, and SVL and TL measured to the nearest mm. Wet gonads and fat bodies were removed, weighed to the nearest 0.01 g, and the largest size class of vitellogenic follicles in both ovaries counted. A random sample of 30 of those oocytes was measured to the nearest 0.01 mm and the average calculated; for three females a smaller size-class of oocytes was also measured. Because the timing of spermiogenesis was previously identified as occurring during winter (Wilson, 1940, 1941; Rose, 1967), males were sacrificed and dissected only from January through May. Samples from male cloacae were examined for the presence of sperm with a light microscope. Data were log-transformed as needed to meet the assumptions of parametric tests (Sokal and Rohlf, 1981). Regression analyses were used to determine relationships between SVL and clutch size, SVL and fat body mass, and between clutch size and fat body mass. Clutch and follic e data were based on the largest size class of yolked oocytes.