FEMALE REPRODUCTIVE-BIOLOGY AND THE COEVOLUTION OF EJACULATE CHARACTERISTICS IN FISH

The influence of female reproductive biology in the evolution of male ejaculate characteristics has received little attention. Fish are an i deal group for investigations of this kind because they exhibit two di screte modes of fertilization (internal versus external) and wide vari ation in both the size and number of gametes produced. Here, using com parative methods, we examine how sperm length, numbers, and longevity are related to ova numbers, size, and the mode of fertilization across fish species. We find that sperm numbers increase with ova numbers am ong externally fertilizing species, fitting the predictions of theoret ical models. However, sperm numbers are apparently not related to ovum size. The sperm of internally fertilizing species are generally longe r than those of externally fertilizing relatives, and sperm length is positively correlated with number of ova (but not ovum size) among ext ernal fertilizers. There is a significant positive association between sperm longevity and ovum diameter in externally fertilizing freshwate r species. Likely explanations for the observed relations between fema le reproductive biology and ejaculate characteristics in fish are disc ussed.