Abstract
In reptiles, the mode of reproduction is typically sexual. However, facultative parthenogenesis occurs in some Squamata, such as Komodo dragon (Varanus komodoensis) and Burmese python (Python bivittatus). Here, we report facultative parthenogenesis in the green anaconda (Eunectes murinus). We found two fully developed female neonates and 17 undeveloped eggs in the oviduct of a female anaconda isolated from other individuals for eight years and two months at Ueno Zoo, Japan. To clarify the zygosity of the neonates, we analyzed 18 microsatellite markers of which 16 were informative. We observed only maternal alleles and no paternal alleles for all 16 markers. To examine the possibility of the long-term sperm storage, we estimated allele frequencies in a putative parental stock by genotyping five unrelated founders. If all founders, including the mother, are originated from a single Mendelian population, then the probability that the neonates were produced by sexual reproduction with an unrelated male via long-term sperm storage was infinitesimally small (2.31E-32 per clutch). We also examined samples from two additional offspring that the mother delivered eight years before her death. We consistently observed paternal alleles in these elder offspring, indicating that the mother had switched from sexual reproduction to asexual reproduction during the eight years of isolation. This is the first case of parthenogenesis in Eunectes to be validated by DNA analysis, and suggests that facultative parthenogenesis is widespread in the Boidae.
Highlights
Among vertebrates, parthenogenesis, the occurrence of unisexual lines whereby reproduction occurs without any involvement of males or their sperm, is most common amongst reptiles
Since facultative parthenogenesis producing only females has been reported in other boid species such as Boa constrictor [5], Epicrates maurus [6] and Epicrates cenchria [7], Type A facultative parthenogenesis is to date the most common form, perhaps the only form, of parthenogenesis in Boidae
Female-biased facultative parthenogenesis has been reported in the Pythonidae–Python bivittatus [4], Python regius and Malayopython reticulatus [8]–suggesting that it is the ancestral state shared in basal Alethinophidia
Summary
Parthenogenesis, the occurrence of unisexual lines whereby reproduction occurs without any involvement of males or their sperm, is most common amongst reptiles. Facultative parthenogenesis (FP), occasional occurrence of parthenogenesis, in individuals of a species that normally reproduce sexually occurs in at least five families—Boidae, Pythonidae, Viperidae, Acrochordidae and Colubridae [1]. Systematic facultative parthenogenesis of some species of insect and other invertebrates is thought to be highly adaptive owing to the high hatching success of unfertilized eggs by automixis [2]. The associated very low hatching rate suggests that this form of parthenogenesis is some form of reproduction error [3]. The low hatching rate can be explained by effects of multiple deleterious variations in the parthenogens, that are maintained as heterozygotes in sexually reproducing populations
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