Browsing by Author "Strydom, Aliki V."
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- ItemSeasonal reproduction and sexual size dimorphism of the African helmeted turtle, Pelomedusa subrufa (family Pelomedusidae)(Stellenbosch : Stellenbosch University, 2001-12) Strydom, Aliki V.; Van Wyk, J. H.; Leslie, Alison J.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: PELOMEDUSA SUBRUFA is a freshwater turtle widely distributed throughout Africa and Madagascar, and is described as a Tropical to Sub-tropical species. 1 examined the female and male reproductive cycles of P. subrufa, over a 20-month period to determine whether they display a typical Tropical to Sub-tropical type reproductive cycle (pre-nuptial) or a typical Temperate Zone type reproductive cycle (post-nuptial). Blood and tissue samples were collected from wild specimens captured in the Western Cape, South Africa and these samples were supplemented by tissue samples obtained from museum specimens. In female P. subrufa seasonal variation in related circulating reproductive hormones in the plasma (estradiol, progesterone, and testosterone) were analyzed using validated ELISA kits. Plasma vitellogenin (yolk precursor produced in liver) was measured using a newly developed universal vitellogenin ELISA for vertebrates (UNIVTG). Ovarian follicles were measured (± 0.1 mm) 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 follicular enlargement (vitellogenesis), ovulation and a gravid period. Seasonal timing of the reproductive cycle coincided with those of other temperate zone freshwater turtles. Vitellogenic recrudescence began in summer (late December), and continued unabated through winter with ovulation 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 eggs being significantly correlated with maternal body size (r = 0.82, P < 0 001). Plasma estradiol and plasma vitellogenin concentrations peaked once during the ovarian cycle, typically coinciding with the period of early- to mid-vitellogenesis in late summer. Plasma testosterone varied throughout the year, but significant increases were measured during the ovulation and mating period in spring. Plasma progesterone concentrations were significantly elevated during the gestation period prior to ovi-position in mid-summer (December). In male P. subrufa spermatogenesis in mature specimens was distinctly seasonal and timing of the reproductive cycle coincided with those of other temperate zone freshwater turtles. Spermatogemc recrudescence began in summer, following emergence from a winter hibernation period (brumation) and spring mating. Peak testicular volume and maximum spermiogemc activity occurred in late summer and early autumn. Testicular regression commenced in autumn through winter. Spermatozoa were abundant in the ducti epididymi throughout the year. Plasma testosterone concentrations peaked once during the testicular cycle, typically coinciding with spermio genes is in late summer, early autumn. Ducti epididymi diameter showed significant variation throughout the year, whereas the epithelial cell height showed no significant seasonal variation. Peak secretory activity coincided with spermiogemc activity and high circulating testosterone concentrations in late summer, early autumn. Testicular recrudescence was correlated with increasing ambient air temperatures, photopenod and summer rainfall, whereas testicular regression, during late autumn, corresponded conversely with decreasing ambient air temperatures, photopenod and rainfall. Female and male reproductive cycles were asynchronous in that the peak spermatogenic activity occurred in autumn at the time when most females were depositing yolk in growing ovarian follicles. Therefore, adult females displayed a typical postnuptial vitellogemc cycle and adult males displayed a typical post-nuptial spermatogenic cycle. Differences between sexes in body size are common in many animals, and the African helmeted 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 significantly larger than adult females. Using carapace length as the measure of body size (covariate), adult males, 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 no significant difference between adult males, adult females and juveniles in head width and head length. 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 of ontogenetic 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 in depth, the adults grow at a faster rate when compared to the juveniles. Adults significantly grow at a faster rate than juveniles in absolute head size as well. However, when these traits were used as a whole data set (eight traits measured), there was no difference in growth rate between adults of either sex. Similarly, there was no significant difference in adults compared to juveniles in shell size, however, adults grow at a faster rate than juveniles in absolute body size and head size. Differences in body size, and in the size of traits such as shell measurements and head measurements relative to absolute body size, were assessed to clarify SSD of P. subrufa in South Africa.