SPERM PRECEDENCE IN EXPERIMENTAL INTERSPECIFIC MULTIPLE MATINGS OF HYBRIDIZING NORTH AMERICAN TIGER SWALLOWTAIL BUTTERFLY SPECIES (LEPIDOPTERA: PAPILIONIDAE)

摘要

Papilio canadensis and P. glaucus have multiply-mating females and males. Laboratory hand-pairings allowed us to by-pass natural mating preferences of polyandrous females and conduct sequential (twice-mated) lab pairings; one heterospecific and one conspecific male for each virgin female of P. glaucus or P. canadensis. Using electrophoresis and species-specific (diagnostic) allozymes, we were able to determine whether random fertilization (a mix of heterospecific sperm) or sperm precedence (either first or last male) existed for these twice-mated females. Since the number of useful double pairings for lab and field female analyses was low, we can only conclude that of double mated females, most are fertilized by males of their first mating, but thata mix of sperm and last male sperm precedence do occur at lower frequencies. Overall, these lab results suggest that if it exists, sperm selection by females of P. glaucus and P. canadensis would not necessarily provide a clear mechanism of reproductiveisolation. In fact, eggs from interspecific primary hybrid lab crosses (73 families of Pg x PC and 17 families of PC x Pg hybrids; all single pairing F_1 crosses) are as fertile and viable as those from parental types. The isolating mechanisms that maintained a narrow hybrid zone from 1980-1997 have not been sustained during the recent 1998-2003 period where extensive interspecific hybrid introgression and X-chromosome recombination has occurred. It is clear that even though lab-reared males were regularly fed a solution of honey water, amino acids, and electrolytes, they were less successful at producing larval offspring that were field-captured (wild) males when mated to virgin females This difference in reproductive success mandates caution in extrapolation from lab to field studies. However lab-reared males can show first male or last male sperm precedence It is also possible for a female to have a mixture of fertilizations from males of different species. We are therefore hesitant to interpret these preliminary results with relatively small sample sizes in the context of sexual selection theory. These results do complicate the interpretation of hybrid zone dynamics.