Caracterização Demográfica, Dimorfismo Sexual, Morfometria e Biologia Reprodutiva de Phrynops geoffroanus (Schweigger, 1812) em duas áreas de Caatinga, Nordeste do Brasil

RESUMO

Este trabalho teve o objetivo de caracterizar demograficamente e morfometricamente uma população do cágado Phrynops geoffroanus, bem como, avaliar seu ciclo reprodutivo em áreas de Caatinga do nordeste brasileiro. Duas áreas do estado da Paraíba foram selecionadas para a coleta de indivíduos RPPN Fazenda Tamanduá foi utilizada para estudar a demografia de uma população em um reservatório temporário; trecho do rio Piranhas-Açú para avaliar o ciclo reprodutivo desses animais. As análises utilizando os indivíduos capturados indicam que não existe diferenças na proporção sexual na população amostrada, bem como, que esta é composta principalmente por indivíduos adultos; e que não existe uma relação significativa entre a quantidade de animais capturados e a quantidade de chuva durante o período amostrado. Quanto a reprodução desta espécie em áreas de caatinga, os indivíduos coletados um trecho do Rio Piranhas-Açu (entre os Estados da Paraíba e Rio Grande do Norte) mostraram que existe um forte dimorfismo sexual, sendo baseada principalmente no maior tamanho das fêmeas. Análises histológicas das gônadas revelaram que fêmeas e machos de P. geoffroanus reproduzem continuamente na área estudada, sem mostrar relação com a precipitação histórica registrada para a região. Este padrão é aqui, identificado pela primeira vez em áreas semiáridas para esta espécie, diferentemente do que é esperado para espécies de ambiente tropicais, onde a pluviosidade é o principal fator ambiental regulador das atividades reprodutivas nos Testudines.

ABSTRACT

This work aimed to demographically and morphometrically characterize a population of Phrynops geoffroanus, as well as to evaluate the reproductive cycle in two areas of Caatinga do Sertão da Paraíba. The first chapter was conducted in an area of Caatinga in the Northern Depression of the State of Paraíba, at RPPN Fazenda Tamanduá. Individuals captured by hand or by pit were measured and weighed. Size and weight were compared between sexes and methods of capture using a MANOVA. Sex ratio was compared between capture methods using Pearson's Chi-square test. Population density and biomass were calculated. The number of animals captured was grouped into three shifts and compared. Throughout the year, 113 individuals were captured in the reservoir, with a population of 43.4% males, 47.8% females and 8.8% juveniles, with a density of at least 41.8 individuals / ha and biomass of 33,05kg/ha. There is no significant relationship between the number of animals captured and the amount of rain during the sampled period. Due mainly to the ephemerality of the aquatic environments of the Caatinga and to the unpredictability of the rains of this biome, the populations of aquatic species present great population variations and in their biological activities. Further studies are needed to fill several gaps in the knowledge of the natural history of Caatinga turtles. The second chapter aimed to describe the reproductive cycle of Phrynops geoffroanus in a semi-arid area of Northeastern Brazil and was carried out in one section of the Piranhas-Açu River, between the States of Paraíba and Rio Grande do Norte, through active search and pit traps. The collections were monthly, between November 2018 and October 2019. The individuals were weighed, measured and sacrificed. For females, the length and width of all eggs found in the oviduct were measured, in addition to the two largest ovarian follicles. For males, testicle length and width were measured to calculate their volume using the ellipsoid formula. Testicles and epididymides were prepared for conventional histological study. 32 females and 41 males were collected throughout the sampling period. There is sexual dimorphism in weight, CCL, CCW, MCL, MCW, AAP, MPL, MPW and TL. The frequencies of reproductive females and males of P. geoffroanus showed no relation to the historical precipitation recorded for the study area. Sexually mature females were recorded over most of the sampled months. The simultaneous presence of vitellogenic follicles and eggs in the oviduct in some females, suggests the production of at least two litters per reproductive season. The average number of eggs per litter was 11.14. In males, only the density of sperm was influenced by precipitation. Animals with few sperm were found in the testicles, explaining this difference in density, but with a lot of sperm in the epididymis. The presence of females with vitellogenic follicles and the presence of males with sperm throughout the year, allows to infer that reproduction of this species in the sampled area is not influenced by rain.