Twice-mated Females Research Articles

The adaptive significance of mate guarding in the soapberry bug,Jadera Haematoloma (Hemiptera: Rhopalidae)

Male soapberry bugs (Jadera haematoloma)face severe mating competition at the northern edge of their range due to male-biased adult sex ratios. Copulations lasting up to 11 days may serve a mate guarding function (encompassing four or more ovipositions), but copulation duration is highly variable, with some pairings lasting as little as 10 min. Data were gathered to describe factors that influence the reproductive costs and benefits of prolonged copulation. Estimated copulation durations (mean ± SD) were 20 ± 23 h in the lab and 50 ± 8 h in the field and were only weakly affected by sex ratio. Females mated for 5 min produced as many fertile eggs as those mated for 600 min laid; they became depleted of fertile sperm after about 25 days. In twicemated females, the first male's paternity was reduced by about 60%, and all females (N = 13) whose mates were removed experimentally mated again within an average of 6 min. The outcome of sperm competition on a perclutch basis was not highly predictable. The possibility of increased sperm displacement in longer copulations was not tested. Males often guarded females during oviposition and successfully defended them from intruding single males by recopulating. Such intrusions occurred in the majority of oviposition attempts observed in nature. Even though most females mated promiscuously, in a focal aggregation with a mean sex ratio of 2.2 ± 0.4 males/female, the interval between matings by males was commonly several days. Males appeared to respond facultatively to several aspects of the distribution and availability of females. The intensities of mating competition and sperm competition indicate that monogamous mate guarding should be favored over nonguarding in nature. Unpredicted brief. pairings may result from assessment by males of female reproductive value or of their own physical condition, or from female resistance.

Sperm Use Patterns of Individual Fall Armyworm (Lepidoptera: Noctuidae)

The incidence of multiple mating and patterns of sperm use were examined in females of the fall armyworm, Spodoptera frugiperda (J. E. Smith), using electrophoretic markers. Thirty-five of 66 females mated more than once. Of these, 27 mated twice, 7 mated three times, and 1 mated four times. Eight twice-mated females and their progeny fit experimental criteria established for subsequent examination of sperm use patterns. Maximum likelihood methods were employed to assign probabilities of paternity to daily progeny groups subsequent to the second mating. Considerable variation was observed among females. Two females continued to produce progeny fathered by sperm from the first mating, four females switched to sperm predominantly from the second mating, and two females produced progeny that exhibited nearly equal paternity. The time interval between first and second matings did not seem to influence sperm use. Female benefits from multiple mating do not appear to be related to sperm replenishment or enhanced reproductive output but may simply be to compensate for the possibility of infertile initial matings.

Estimating the degree of sperm precedence in laboratory mating experiments: a maximum likelihood method.

Allozyme polymorphisms have been used frequently in laboratory mating experiments to study patterns of sperm utilization in multiply mated females. In some instances, due either to chance or to design, there is a diagnostic difference between male genotypes that allows unambiguous assignment of paternity. In other instances, there is some overlap in allelic composition of males, so that attribution of paternity is often uncertain. This paper presents a statistical method for analyzing data of the second sort obtained from twice-mated females, based on the principle of maximum likelihood. The method allows the estimation of a mating parameter, psi the frequency with which sperm from the first male fertilizes the female's eggs. Various hypotheses about the null value of psi may be tested by a likelihood ratio test statistic. Also presented is a method of testing for homogeneity in psi values across different broods produced by the same female.

Variation in Laboratory Oviposition by Rhagoletis pomonella (Diptera: Tephritidae) in Relation to Mating Status

In the laboratory, females of R. pomonella were allowed to mate once, twice, or multiply, and to oviposit into artificial fruit. Females mated once did not differ from virgin females in total fecundity, rate of egg laying, or egg-laying longevity. Twice-mated and multiply-mated females had significantly greater total fecundity and demonstrated trends toward higher egg-laying rate and egg-laying longevity than virgin and once-mated females. Average female fertility increased and was maintained at a higher level over time with more matings. Female R. pomonella require multiple matings to achieve maximal reproduction (total number of hatching eggs) in the laboratory, apparently because sperm depletion occurs. In addition, increased oviposition results from behavioral interactions among R. pomonella individuals