Reproduction in dwarf chameleons (Bradypodion) with particular reference to B. pumilum occurring in fire-prone fynbos habitat

[摘要] ENGLISH ABSTRACT: South Africa, Lesotho and Swaziland are home to an endemic group of dwarfchameleons (Bradypodion). They are small, viviparous, insectivorous, arboreallizards, found in a variety of vegetation types and climatic conditions. Previouswork on Bradypodion pumilum suggests prolonged breeding and high fecunditywhich is very unusual for a viviparous lizard inhabiting a Mediterraneanenvironment. It has been suggested that the alleged prolonged reproductionobserved in B. pumilum may be a reproductive adaptation to life in a fire-pronehabitat. In addition, Chamaesaura anguina a viviparous, arboreal grass lizard alsooccurs in the fire-frequent fynbos and exhibits an aseasonal female reproductivecycle with high clutch sizes; highly unusual for the Cordylidae. With theobservation of two species both inhabiting a fire-driven environment and exhibitingaseasonal reproductive cycles with high fecundity, it was thought that thisunpredictable environment may shape the reproductive strategies of animalsinhabiting it. However, detailed reproductive data for B. pumilum were unavailable.The first aim was provide baseline reproductive data for B. pumilum and to discussthe reproductive strategy in relation to a fire-prone environment. To establish thesignificance of fire in the reproductive strategy of B. pumilum, reproductive data ofother Bradypodion species, not inhabiting the fire-prone area was required. Thesecond aim was to provide baseline reproductive data for Bradypodion withdiscussion on possible scenarios facilitating the evolution of dwarf chameleonreproduction. Bradypodion pumilum specimens were collected in monthly samplesfrom Stellenbosch and Somerset West in the Western Cape, South Africa.Specimens of other Bradypodion species were obtained from South Africanmuseums. Data were collected for both sexes of Bradypodion, and sperm storage ability was investigated in B. pumilum. Bradypodion females all showed anaseasonal reproductive cycle with relatively high clutch sizes for their body sizeand the possibility of individual females producing multiple clutches per year. MaleBradypodion have sperm available the entire year round however, there appearsto be an increase in sperm production in autumn and again in spring in B.pumilum. Elements of this bimodal pattern are seen in other Bradypodion species.Dwarf chameleons regardless of habitat and associated climatic conditions arethus able to reproduce through out the year. It has also been demonstrated in B.pumilum that both sexes are able to store sperm and it is expected that otherBradypodion species would posses this character. This type of reproductivestrategy is highly unusual for viviparous, temperate-zone lizards. It is likely that thecooling of the climate due to the development of the Benguela current facilitatedthe transition to viviparity in Bradypodion. Bradypodion may be aseasonalreproducers for a number of reasons. They are of tropical ancestry, they relativelyrecently inhabited tropical forests, or fluctuations in climate may have caused this.Bradypodion most likely have a high reproductive output due to their intensevulnerability to predation as in other chameleon species. The proposed hypothesisthat the unusual reproductive characteristics of B. pumilum (and possibly theancestral Bradypodion) were due to inhabiting a fire-prone environment nowappears an unlikely explanation. However, even if this extraordinary reproductionwas not in direct response to fire, the strategy appears beneficial in this type ofunpredictable environment.

[发布机构] Stellenbosch University