ABSTRACT
Reproductive seasonality is common among snakes, with mating, pregnancy, and birth or oviposition occurring only during few months of the year and modulated mainly by two environmental phenomena—temperature and rainfall. Species of Bothrops inhabit regions with varied climatic conditions, including those that are tropical, subtropical, equatorial, and semiarid. Bothrops atrox is an endemic and widespread species of the Amazon rain forest. Such habitat is characterized by an equatorial climate with little variability in temperature and humidity, but marked seasonality in intense precipitation. We investigated several aspects of the reproductive biology of B. atrox, including the reproductive cycle, the sexual segment of the kidney (SSK), sperm storage, and the possible influence of temperature and rainfall on pregnancy duration, birth, and spermatogenesis. Specifically, we examined museum specimens to describe sexual dimorphism, litter size, and male and female urogenital cycles through macroscopic and histological analyses. Females of B. atrox exhibited follicular recrudescence mainly from January to April (part of the wet season). Pregnant females were found throughout the year (except May), but births were found to occur mainly at the end of the dry season (August–October). Males exhibited SSK hypertrophy and sperm production in the wet season (November–April). Females were found to be larger than males, but males of B. atrox—as with other members of the B. atrox species complex—obtain relatively larger body sizes when compared with other species of Bothrops, which might be an adaptive response to male–male combat in this species. Together, our results show that B. atrox from Amazonia has a unique reproductive strategy (for each sex) among pit vipers, indicating greater reproductive plasticity when compared with its congeners.
ABSTRACT
As serpentes Bothriopsis bilineatus e Bothrops atrox são viperídeos simpátricos na Amazônia, sendo B. atrox comum e B. bilineatus mais rara. Ambas espécies apresentam uma dieta generalista, sendo que B. atrox forrageia principalmente sobre o chão e B. bilineatus é mais arborícola. Aqui, nós descrevemos o uso do habitat e padrão de atividade dessas duas serpentes em uma floresta amazônica no Rio Moa, Cruzeiro do Sul, Acre. Esse estudo foi baseado em observações durante procura visual limitada por tempo e encontros ocasionais de serpentes em uma trilha que é sazonalmente alagada e outra de floresta de terra firme. Durante um total de 360 horas de procura visual limitada por tempo, 11 B. bilineatus e seis B. atrox foram encontradas, enquanto uma B. bilineatus e seis B. atrox foram encontradas durante encontros ocasionais. Todas 12 B. bilineatus foram observadas sobre a vegetação, enquanto somente cinco B. atrox estavam sobre a vegetação (todos juvenis). Durante procura visual limitada por tempo B. bilineatus foi mais comum (0,03 serpentes/hora) do que B. atrox (0,016 serpentes/hora). Essas duas espécies apresentaram diferenças no uso do espaço, sendo que B. bilineatus ocorreu principalmente na área da floresta de terra firme, rica em palmeiras e que não é sazonalmente alagada. Bothrops atrox foi mais abundante na área da floresta próxima aos lagos, que é sazonalmente alagada. Diferenças entre essas duas áreas como a estrutura da vegetação, tipos de ambientes aquáticos, disponibilidade de presas e fatores históricos são possivelmente os fatores responsáveis pela diferença na ocorrência dessas espécies. Estas duas serpentes foram encontradas nos meses mais chuvosos e não foram registradas nos meses mais secos, período em que também existe menor disponibilidade de anuros nesses ambientes. Na maior parte da Amazônia, B. bilineatus parece ser menos frequente que B. atrox, mas na área do presente estudo, a primeira parece ser mais frequente que a última durante procura visual limitada por tempo.
The snakes Bothriopsis bilineatus and Bothrops atrox are sympatric vipers in the Amazon. While B. atrox is common, Bothriopsis bilineatus is considered relatively rare. Both species are dietary generalists, with B. atrox foraging mostly on the ground while B. bilineatus is more arboreal. Here, we describe habitat use and activity patterns for these two snakes in Amazonian forest near the Moa River, Cruzeiro do Sul (Acre). This study was based on observations during both time constrained visual searches and opportunistic encounters along trails that included both seasonally flooded and terra firme forests. During a total of 360 hours of time constrained visual search, 11 B. bilineatus and six B. atrox were found, while one B. bilineatus and six B. atrox were found during opportunistic encounters. All 12 B. bilineatus were found on vegetation above the ground, while only five B. atrox were on vegetation, and these were all juveniles. Thus, during time constrained visual searches B. bilineatus was more common (0.03 snake/hour) than B. atrox (0.016 snake/hour). These two species use different habitats. Bothriopsis bilineatus was most commonly found in upland terra firme forests, with many palms and free from seasonal floods. Bothrops atrox was most commonly found in lower, wetter seasonally flooded areas. Perhaps structural differences in the vegetation in these two forest types influence the distribution of these two species, possibly due to a related influence on prey abundance, besides historical factors. Both species are found more often during the rainy season, rarely being found during the dry season, when their amphibian prey are less abundant. In most of the Amazon, B. bilineatus seems less common than B. atrox, but in the present study, the former was the most frequent snake during time constrained visual search.
ABSTRACT
We studied the defensive strike of one species of each of five recognized lineages within the genus Bothrops, namely, B. alternatus, B. jararaca, B. jararacussu, B. moojeni and B. pauloensis. The defensive strike of the studied species was in general similar to that of Crotalus viridis and C. atrox, but some important differences were observed. Bothrops alternatus and B. pauloensis struck preferentially from a tight body posture, whereas B. jararaca and B. moojeni from a loose body posture. Defensive strikes were either true or false (during the latter, the mouth remains closed or partially open). Almost all strikes were successful; only on a few occasions snakes missed their target (flawed strikes). Strike variables were very conservative among the five species, especially strike distance and height, and one possible explanation may be related to constraints imposed on strike variables as a way of increasing strike accuracy.
Estudamos o bote defensivo de uma espécie de cada uma de cinco reconhecidas linhagens do gênero Bothrops, a saber: B. alternatus, B. jararaca, B. jararacussu, B. moojeni e B. pauloensis. O bote defensivo das espécies estudadas foi, em geral, semelhante ao de Crotalus viridis e C. atrox, porém algumas diferenças foram observadas. Bothrops alternatus e B. pauloensis desferiram botes preferencialmente a partir de postura corpórea enrodilhada, ao passo que B. jararaca e B. moojeni desferiram a maioria dos botes a partir de postura corpórea frouxa. Os botes defensivos foram verdadeiros ou falsos (nestes, a boca da serpente permaneceu fechada ou parcialmente aberta). Quase todos os botes foram bem-sucedidos; apenas em alguns casos a serpente errou o alvo (botes falhos). As variáveis relativas aos botes foram bastante conservativas entre as cinco espécies, principalmente distância e altura do bote, e uma possível explicação pode estar relacionada a restrições impostas às variáveis relativas aos botes como forma de aumentar sua acurácia.
Subject(s)
Animals , Bothrops/physiology , Escape Reaction/physiology , Bothrops/classification , Escape Reaction/classificationABSTRACT
We studied the defensive strike of one species of each of five recognized lineages within the genus Bothrops, namely, B. alternatus, B. jararaca, B. jararacussu, B. moojeni and B. pauloensis. The defensive strike of the studied species was in general similar to that of Crotalus viridis and C. atrox, but some important differences were observed. Bothrops alternatus and B. pauloensis struck preferentially from a tight body posture, whereas B. jararaca and B. moojeni from a loose body posture. Defensive strikes were either true or false (during the latter, the mouth remains closed or partially open). Almost all strikes were successful; only on a few occasions snakes missed their target (flawed strikes). Strike variables were very conservative among the five species, especially strike distance and height, and one possible explanation may be related to constraints imposed on strike variables as a way of increasing strike accuracy.
Estudamos o bote defensivo de uma espécie de cada uma de cinco reconhecidas linhagens do gênero Bothrops, a saber: B. alternatus, B. jararaca, B. jararacussu, B. moojeni e B. pauloensis. O bote defensivo das espécies estudadas foi, em geral, semelhante ao de Crotalus viridis e C. atrox, porém algumas diferenças foram observadas. Bothrops alternatus e B. pauloensis desferiram botes preferencialmente a partir de postura corpórea enrodilhada, ao passo que B. jararaca e B. moojeni desferiram a maioria dos botes a partir de postura corpórea frouxa. Os botes defensivos foram verdadeiros ou falsos (nestes, a boca da serpente permaneceu fechada ou parcialmente aberta). Quase todos os botes foram bem-sucedidos; apenas em alguns casos a serpente errou o alvo (botes falhos). As variáveis relativas aos botes foram bastante conservativas entre as cinco espécies, principalmente distância e altura do bote, e uma possível explicação pode estar relacionada a restrições impostas às variáveis relativas aos botes como forma de aumentar sua acurácia.