Last male sperm precedence in a damselfly demonstrated by RAPD profiling

The effect of male-male competition and ornament size on mean and variance of courtship intensity towards heterospecific and conspecific females

Discrimination between hetero- and conspecifics is the elementary choice an individual performs when searching for potential mates. The level of selectivity and strength of species discrimination is modified by variance in the quality of females, level of the male’s reproductive investment, mate search costs, and the competitive environment. The effect of the competitive environment on both species discrimination and conspecific mate choice has seldom been studied simultaneously. We experimentally manipulated territorial competition ofCalopteryx splendensdamselfly males in the wild, and asked two questions. First, does increased competition influence the territorial males’ responses towards introduced heterospecificC. virgofemales. The effect of the size of the territorial males’ sexual ornaments (wing spot) on their responses towards females was also investigated. Second, does increased competition influence the territorial males’ response towards conspecific females? The effect of the size of the territorial males ornament was again investigated. The mean level of response towards heterospecific females did not change between the control (i.e., no competitors presented) and the competition (i.e., two competitors presented) treatments, but the variance of responses towards heterospecifics was greater in the competition treatment. The territorial males’ responses towards conspecific females did not change between control and competition treatments. These results indicate individual differences in the behavior of males towards heterospecifics when territorial competition was experienced. The observed pattern of discrimination might be adaptive when overall reproductive success is considered.

Comparison of microsatellites and amplified fragment length polymorphism markers for parentage analysis

This study compares the properties of dominant markers, such as amplified fragment length polymorphisms (AFLPs), with those of codominant multiallelic markers, such as microsatellites, in reconstructing parentage. These two types of markers were used to search for both parents of an individual without prior knowledge of their relationships, by calculating likelihood ratios based on genotypic data, including mistyping. Experimental data on 89 oak trees genotyped for six microsatellite markers and 159 polymorphic AFLP loci were used as a starting point for simulations and tests. Both sets of markers produced high exclusion probabilities, and among dominant markers those with dominant allele frequencies in the range 0.1-0.4 were more informative. Such codominant and dominant markers can be used to construct powerful statistical tests to decide whether a genotyped individual (or two individuals) can be considered as the true parent (or parent pair). Gene flow from outside the study stand (GFO), inferred from parentage analysis with microsatellites, overestimated the true GFO, whereas with AFLPs it was underestimated. As expected, dominant markers are less efficient than codominant markers for achieving this, but can still be used with good confidence, especially when loci are deliberately selected according to their allele frequencies.

Molecular genetic analysis of sperm competition in the damselfly Ischnura elegans (Vander Linden)

Sperm competition can be a powerful selective force in the evolution of mating systems. Several odonate species have attracted study to assess the extent and mechanism of last-male sperm precedence. Members of the genus Ischnura (Zygoptera) display a particularly interesting range of mating systems, and Ischnura elegans was selected for study. Polymorphic microsatellites were cloned, sequenced and used to determine paternity of I. elegans larvae, to reveal patterns of sperm precedence. More than 3000 larvae, collected from both wild and captively bred I. elegans females, were typed for one or two microsatellite loci and paternity was determined by comparison with parental genotypes. Microsatellite typing showed that most wild-caught females had mated with several males. Analysis of offspring from females which mated in captivity showed that multiple-matings result in a large proportion of last-male sperm precedence (mean value for immediate last male precedence is 0.79 +/- 0.2 (+/- s.d.; n = 11, range = 0.44-1)). There is appreciable variation in the extent and patterns of immediate and longer-term precedence, which could reflect differences in male sperm removal ability or selective use of sperm by females.