Seasonal reproduction and sexual size dimorphism of the African helmeted turtle, Pelomedusa subrufa (family Pelomedusidae)

[摘要] ENGLISH ABSTRACT:PELOMEDUSA SUBRUFA is a freshwater turtle widely distributed throughout Africa andMadagascar, and is described as a Tropical to Sub-tropical species. 1 examined the female andmale reproductive cycles of P. subrufa, over a 20-month period to determine whether theydisplay a typical Tropical to Sub-tropical type reproductive cycle (pre-nuptial) or a typicalTemperate Zone type reproductive cycle (post-nuptial). Blood and tissue samples were collectedfrom wild specimens captured in the Western Cape, South Africa and these samples weresupplemented by tissue samples obtained from museum specimens.In female P. subrufa seasonal variation in related circulating reproductive hormones inthe plasma (estradiol, progesterone, and testosterone) were analyzed using validated ELISA kits.Plasma vitellogenin (yolk precursor produced in liver) was measured using a newly developeduniversal vitellogenin ELISA for vertebrates (UNIVTG). Ovarian follicles were measured (± 0.1mm) and female ovaries were staged macroscopically (non-active, pre-vitellogenic, vitellogenic,gravid), and results were confirmed via histological sectioning of ovaries and oviducts.Females exhibited a cyclic reproductive pattern, with distinct phases of follicularenlargement (vitellogenesis), ovulation and a gravid period. Seasonal timing of the reproductivecycle coincided with those of other temperate zone freshwater turtles. Vitellogenicrecrudescence began in summer (late December), and continued unabated through winter withovulation occurring in the following spring (September-October). My data suggested that P.subrufa females mostly lay a single clutch of eggs during the late-spnng summer period(September through January). Clutch size varied between 7 -3 7 eggs, with the number of eggsbeing significantly correlated with maternal body size (r = 0.82, P < 0 001). Plasma estradioland plasma vitellogenin concentrations peaked once during the ovarian cycle, typically coinciding with the period of early- to mid-vitellogenesis in late summer. Plasma testosteronevaried throughout the year, but significant increases were measured during the ovulation andmating period in spring. Plasma progesterone concentrations were significantly elevated duringthe gestation period prior to ovi-position in mid-summer (December).In male P. subrufa spermatogenesis in mature specimens was distinctly seasonal andtiming of the reproductive cycle coincided with those of other temperate zone freshwater turtles.Spermatogemc recrudescence began in summer, following emergence from a winter hibernationperiod (brumation) and spring mating. Peak testicular volume and maximum spermiogemcactivity occurred in late summer and early autumn. Testicular regression commenced in autumnthrough winter. Spermatozoa were abundant in the ducti epididymi throughout the year. Plasmatestosterone concentrations peaked once during the testicular cycle, typically coinciding withspermio genes is in late summer, early autumn. Ducti epididymi diameter showed significantvariation throughout the year, whereas the epithelial cell height showed no significant seasonalvariation. Peak secretory activity coincided with spermiogemc activity and high circulatingtestosterone concentrations in late summer, early autumn. Testicular recrudescence wascorrelated with increasing ambient air temperatures, photopenod and summer rainfall, whereastesticular regression, during late autumn, corresponded conversely with decreasing ambient airtemperatures, photopenod and rainfall. Female and male reproductive cycles were asynchronousin that the peak spermatogenic activity occurred in autumn at the time when most females weredepositing yolk in growing ovarian follicles. Therefore, adult females displayed a typical postnuptialvitellogemc cycle and adult males displayed a typical post-nuptial spermatogenic cycle.Differences between sexes in body size are common in many animals, and the Africanhelmeted turtle is no exception. Sexual size dimorphism (SSD) in P. subrufa was pronounced, and using principal component analysis, it was clear that adult male P. subrufa was significantlylarger than adult females. Using carapace length as the measure of body size (covariate), adultmales, adult females, and juveniles differed significantly in absolute size of the carapace width,carapace depth, plastron length, plastron width, and head depth. However, there was nosignificant difference between adult males, adult females and juveniles in head width and headlength. Therefore, adult males were larger than adult females in the seven traits measured,except in carapace depth where the females were significantly larger In the occurrence ofontogenetic growth patterns, the adults grow at a slower rate than juveniles in plastron length.There was no significant difference between adults and juveniles in shell width, however indepth, the adults grow at a faster rate when compared to the juveniles. Adults significantly growat a faster rate than juveniles in absolute head size as well. However, when these traits were usedas a whole data set (eight traits measured), there was no difference in growth rate between adultsof either sex. Similarly, there was no significant difference in adults compared to juveniles inshell size, however, adults grow at a faster rate than juveniles in absolute body size and headsize. Differences in body size, and in the size of traits such as shell measurements and headmeasurements relative to absolute body size, were assessed to clarify SSD of P. subrufa in South Africa.

[发布机构] Stellenbosch University