Reproductive biology of the onychophoran Euperipatoides rowelli

Abstract

The reproductive biology of the ovoviviparous peripatus Euperipatoides rowelli was investigated from field collections and laboratory cultures. The sexes have different demographics. The frequency distribution of individual weight is essentially L-shaped in females, but closer to normality for males: thus the sexes must exhibit different patterns of growth and/or mortality. Males are generally much smaller and rarer than females. The primary sex ratio seems to be 1:1 with equal investment in the sexes, while the tertiary ratio is highly female-biased. Logs with fewer individuals tend to be male-biased while well-populated logs tend to be female-biased. Males mature at 15–30% of the bodyweight of mature females. The weight frequency distribution of males without developed sperm in their tracts is strongly skewed to the lower weights, while that of males with sperm is more normally distributed, indicating that sperm production occurs as soon in life as possible. Males mature in their first year of life, if growth rates in culture may be extrapolated to the wild. In contrast to this rapid maturity in males, females may mature as late as their second or third years. Most mature females, and many prior to maturity, carry sperm in their spermathecae. After maturity, there is an approximately linear relationship between body mass and number of developing embryos. Reproduction in E. rowelli is significantly seasonal despite high individual variance, with a major bout of parturition in November–December (summer). A female can harbour one developed and one undeveloped batch of embryos in each uterus. Excesses of developed embryos in one uterus are counterbalanced by deficits of undeveloped ones, indicating that females can use their paired reproductive tracts independently. Individual females in culture can experience episodes of parturition approx. 6 months apart without re-mating, thus gestation may be 6 months or more. Sperm in spermathecae remain capable of vigorous swimming for at least 9.5 months.