Reproductive biology of the onychophoran Euperipatoides rowelli

The reproductive biology of the ovoviviparous peripatus Euperipatoides rowe lli was investigated from field collections and laboratory cultures. The se xes have different demographics. The frequency distribution of individual w eight 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 tertiar y ratio is highly female-biased. Logs with fewer individuals tend to be mal e-biased while well-populated logs tend to be female-biased. Males mature a t 15-30% of the bodyweight of mature females. The weight frequency distribu tion of males without developed sperm in their tracts is strongly skewed to the lower weights, while that of males with sperm is more normally distrib uted, 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, fem ales may mature as late as their second or third years. Most mature females , and many prior to maturity, carry sperm in their spermathecae. After matu rity, there is an approximately linear relationship between body mass and n umber of developing embryos. Reproduction in E. rowelli is significantly se asonal despite high individual variance, with a major bout of parturition i n November-December (summer). A female can harbour one developed and one un developed 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. Indiv idual females in culture can experience episodes of parturition approx. 6 m onths apart without re-mating, thus gestation may be 6 months or more. Sper m in spermathecae remain capable of vigorous swimming for at least 9.5 mont hs.