Speciation and reproduction in the Heteronotia binoei complex (Reptilia: Gekkonidae) with reference to parasite infection

Abstract

The Heteronotia (Gekkonidae) genus is revised, resulting in the description of four new species. It is proposed that H. binoei, the previously widespread species occurring across much of Australia, is now restricted to two isolated areas. Three of the newly described species have affinities with the bisexual H. binoei, one of which is bisexual (H. deserticola sp.nov.) and two are parthenogenetic (H. darevskyi sp.nov. and H. occidentalis sp.nov.) . The fourth new species, H. fasciolatus sp.nov., is a boldly banded bisexual Heteronotia from the Central Ranges region and, can be distinguished from all other Heteronotia species by a unique head pattern. Two species (H. anomala, H. derbianus) have been also resurrected from synonymy of H. binoei. Morphologically all six species in the H. binoei species complex are very similar and could not be distinguished with the characters used. The six species, however, are allopatric in respect to each other, with only narrow overlap zones. This enables most Heteronotia specimens to be identified within their known geographical range. Under semi-natural conditions, reproduction by female H. binoei and parthenogenetic Heteronotia is very seasonal, with gravid females found in October and egg laying occurring in November and December. Approximately 49% of females (42% of the H. binoei and 53% of the parthenogenetic females) in the semi-natural populations were reproductively active during two breeding seasons, each producing two eggs. Only five (7.4%) eggs hatched during this experiment (two H. binoei and three parthenogenetic Heteronotia) and, all five hatchlings failed to survive the first three months. The cause of this low hatching and survival rate is unknown. Reproduction by female Heteronotia in natural populations is similar (as determined by the examination of the reproductive status of museum specimens), though reproductively active females are found from July to March. The cause of this extended breeding season in natural populations may be related to year-to-year variation in the timing of reproduction in response to environmental conditions. Most of the adult male Heteronotia from all four species investigated, contain mature sperm, suggesting that spermatogenesis is continuous and that males are capable of reproducing throughout the year. The similarity in the reproductive potential (as measured by egg production) between the bisexual and parthenogenetic Heteronotia suggest that the parthenogenetic Heteronotia have a two-fold reproductive advantage. This advantage is attributable to bisexual Heteronotia producing male offspring. If this is the case, the parthenogenetic females may be expanding their distribution at the expense of the bisexual species. However, at present there is insufficient evidence to conclude if the parthenogenetic females do have this reproductive advantage as egg and offspring viability is unknown. The two fold reproductive advantage of the parthenogenetic females may be also reduced, due to their higher susceptibility to parasite infections, particularly Isospora coccidia and Geckobia mites, compared to the bisexual Heteronotia. The present day distribution of parthenogenetic Heteronotia may also reflect the colonisation of areas void of bisexual Heteronotia. The parthenogenetic females may have a higher relative fitness in the areas due to the absence of interactions (competitive or behavioural) with bisexual Heteronotia.