Parental Investment and Sex Allocation in a Viviparous Onychophoran

Abstract

Although viviparous reproduction is employed by species in at least six different animal phyla it is rarely common. The phylum Onychophora is exceptional as most of the species are viviparous. Limited information is available on reproductive biology of this group. The current study provides information on parental investment and sex allocation in natural populations of Neotropical Plicatoperipatus jamaicensis. Gravid females of this onychophoran showed an average maternal effort of 12.6% (maximum 34.0%) and carried from 1-4 embryos of varying developmental stage, suggesting that offspring are born individually rather than in clutches. There was considerable overlap in the size distributions of freeliving juveniles and embryos, indicating that the period of embryonic care is variable. There was a positive correlation between embryo and maternal size, suggesting that large females release larger offspring which can more quickly attain maturity. Males of this species were sexually mature shortly after birth. Females were inseminated while small, but then had to undergo substantial growth before reproduction. Sex ratios of juveniles and adults were significantly female-biased, but embryos showed a 1:1 sex ratio. Sex ratios of broods approximated binomial expectations, and there was no shift in sex ratio with female size, suggesting that offspring gender is not maternally controlled.