Like adaptation to the environment and predation, reproduction is an integral part of the survival of species.
The yolk constitutes the energy reserves used by embryos during embryonic development. It is produced by the maternal organism and accumulates in the oocyte during oogenesis (Wikipedia). It usually takes place during the active snake period.
Spermatogenesis is the process of sperm production, which takes place in the seminiferous tubules of the testes. It encompasses the phenomena which, spermatogonia, diploid stem cells (2n chromosomes), lead to spermatozoa, male gametes haploid (n chromosomes). (Wikipedia)
The weather conditions and the presence of potential prey are crucial factors and directly influence the breeding periods and therefore the gestation or incubation times.
Cool temperate regions
Summer is the main activity period for snakes, but it is too short to complete a breeding cycle. Vitellogenesis therefore takes place in the spring.
Warm temperate regions
Although the winters are mild, the summer is longer and because of this, the breeding cycle can take place without interruption.
The dry season of winter and spring are unfavorable to birth. In this period there will be only spermatogenesis and sometimes vitellogenesis.
The equatorial regions
There are usually no distinct periods during the year for breeding, but rising temperatures in the spring usually serve as a chronological indicator.
Just before breeding, T. albolabris males observe the female about 7-10 cm apart (Personal Observation, 2016-2017, Devan-Song, E. A. (2014)).
It has been observed, particularly in the green species of the complex, that they were able to recognize each other, thus avoiding hybridization through behavioral differences (Sanders, KL, Malhotra, A., & Thorpe, RS (2006) ).
Except for the oviparous species presented in the table below, all Trimeresurus are viviparous (Das, I. (2015)).
The breeding period is dependent on the biotope in which the breeding pair lives. To be able to reproduce, the male and the female must have reached sexual maturity. The latter is no longer expressed in age, as it was at one time, but in size. To be sexually mature, the individual must have some SVL (snout-venth length in English, the length between the muzzle and the cloaca). In Trimeresurus albolabris, the SVL of males is on average 350mm with a variation between 330 and 365 mm. Females have an average SVL of 470mm with a variation between 446 and 492 mm. Their respective sexual maturity, expressed in SVL is 410mm for males and 460mm for females. These will probably not happen again, however, until they reach 520mm. In comparison, T. stejngeri is sexually mature at around 370 mm SVL (Devan-Song, E.A. (2014), Devan-Song, A., Martelli, P., & Karraker, N.E. (2017)).
In Hong Kong, China, male T. albolabris individuals reach sexual maturity at 410mm while females that appear to reproduce at 520mm reach around 460mm. Mating takes place between August and October, which coincides with spermatogenesis. Sperm storage is done during winter, gestation during the summer, and parturition between late July and early August (Devan-Song, A., Martelli, P., & Karraker, NE (2017)). ).
Breeding occurs 1x per year for females, sometimes less often, but larger ones are able to reproduce 2x in the same year (Devan-Song, EA (2014), Devan-Song, A., Martelli, P. , & Karraker, NE (2017)).
For species that live in a wintering environment, it is not uncommon to see multiple individuals at the same site (Devan-Song, E.A. (2014)).
Several studies on Viridovipera stejnegeri and Trimeresurus albolabris have demonstrated that females were able to store sperm for 1 year (Tsai, T.S., & Tu, M.C. (2001), Devan-Song, E.A. (2014)).
In recorded births, no study was able to show a significant differential ratio between males and females that could be informed of higher energy production for either sex. Moreover, the microhabitat of Viridovipera stejnegeri remains the same whether gravid or not (Wang, S., Lin, H.C., & Tu, M.C. (2003)).
Observations of three reproduction of Trimeresurus macrops, one on the ground and two within 1m50 of the soil were carried out in the course of the year 2017. The duration of the reproductions varied between 2.2 hours and 12.9 hours. That said, the authors report that the observation was made after the start of mating in two of the three observations (STRINE, Colin, BROWN, Andrew, BARNES, Curt, et al., 2017). The duration could therefore be longer. Males use aggressive bodily behaviors to reproduce but the study does not reveal how far. Females pull males into branches (Personal Observation, 2015, STRINE, Colin, BROWN, Andrew, BARNES, Curt, et al., 2017)
The different species that coexist are able to identify themselves thanks to distinct behaviors (Sanders, K.L., Malhotra, A., & Thorpe, R.S. (2006)).
Male reproductive organs
For scientists, and described by the herpetologist Clifford Pope (1899-1974), hemipenias allow species identification and classification (Malhotra, A., & Thorpe, R. S. (2004)).
Devan-Song, E. A. (2014). Ecology and conservation of the bamboo pit viper: Natural history, demography and effects of translocation.
Tsai, T. S., & Tu, M. C. (2000). Reproductive cycle of male Chinese green tree vipers, Trimeresurus s. stejnegeri, in northern Taiwan. Journal of Herpetology, 424-430.
Tsai, T. S., & Tu, M. C. (2001). Reproductive cycle of female Chinese green tree vipers, Trimeresurus stejnegeri stejnegeri, in northern Taiwan. Herpetologica, 157-168.
Devan-Song, A., Martelli, P., & Karraker, N. E. (2017). Reproductive Biology and Natural History of the White-lipped Pit Viper (Trimeresurus albolabris Gray, 1842) in Hong Kong. Herpetological Conservation and Biology, 12, 41-55.
Sanders, K. L., Malhotra, A., & Thorpe, R. S. (2006). Evidence for a Müllerian mimetic radiation in Asian pitvipers. Proceedings of the Royal Society of London B: Biological Sciences, 273(1590), 1135-1141.
Malhotra, A., & Thorpe, R. S. (2004). A phylogeny of four mitochondrial gene regions suggests a revised taxonomy for Asian pitvipers (Trimeresurus and Ovophis). Molecular Phylogenetics and Evolution, 32(1), 83-100.
Wang, S., Lin, H. C., & Tu, M. C. (2003). Skewed sex ratio of the Chinese green tree viper, Trimeresurus stejnegeri stejnegeri, at Tsaochiao, Taiwan. ZOOLOGICAL STUDIES-TAIPEI-, 42(2), 379-379.
DAVID, P., VOGEL, G., PAUWELS, O. S., & VIDAL, N. (2017). Description of a new species of the genus Trimeresurus from Thailand, related to Trimeresurus stejnegeri Schmidt, 1925 (Serpentes, Crotalidae). Tropical Natural History, 2(1), 5-19.
Das, I. (2015). A field guide to the reptiles of South-East Asia. Bloomsbury Publishing.
Sanders, K. L., Malhotra, A., & Thorpe, R. S. (2004). Ecological diversification in a group of Indomalayan pitvipers (Trimeresurus): convergence in taxonomically important traits has implications for species identification. Journal of Evolutionary Biology, 17(4), 721-731.
MURPHY, R. W. Testing an alternative capture-analysis-release approach to document the reptile fauna of Hon Ba Nature Reserve, central Vietnam.
STRINE, Colin, BROWN, Andrew, BARNES, Curt, et al. Arboreal Mating Behaviors of the Big-Eyed Green Pit Viper (Trimeresurus macrops) in Northeast Thailand (Reptilia: Viperidae). Current Herpetology, 2018, vol. 37, no 1, p. 81-87.