Female Fertilization Success Research Articles

Warmer temperatures result in maladaptive learning of sexual preferences

Abstract The impact of learning ability and sexual selection on the climate and biodiversity crisis is currently unclear. Using the African butterfly Bicyclus anynana, which shows strong phenotypic plasticity (i.e., polyphenism) in response to temperature, we tested whether learning affects mate preferences under climate warming. We first modelled climate warming scenarios and then showed experimentally that temperature becomes an unreliable cue to the onset of the dry season, adult butterflies displayed the wet season rather than the dry season form. Experienced females that were exposed to different male seasonal phenotypes during sexual maturation changed sexual preferences. Female fertilization success was reversed for naive compared with experienced females, likely reducing female fitness following climate warming. Our results emphasize the importance of sexual selection, learning, and their fitness consequences for understanding (mal)adaptation of natural populations to climate warming. Read the free Plain Language Summary for this article on the Journal blog.

Density-dependent sexual selection in external fertilizers: variances in male and female fertilization success along the continuum from sperm limitation to sexual conflict in the sea urchin Strongylocentrotus franciscanus.

Sperm competition and female choice are fundamentally driven by gender differences in investment per offspring and are often manifested as differences in variance in reproductive success: males compete and have high variance; most females are mated and have low variance. In marine organisms that broadcast spawn, however, females may encounter either sperm limitation or sperm competition. I measured the fertilization success of male and female Strongylocentrotus franciscanus over a range of population densities using microsatellite markers. Female fertilization success first increased and then decreased with mate density, limited at low density by sperm limitation and at high density by polyspermy. Mate density affected variance in fertilization success in both males and females. In males, the variance in fertilization success increased with mate density. In females, the pattern was more complex. The variance in female success increased similarly to males with increased mate density but then decreased to low levels at intermediate densities, where almost all eggs were fertilized. As density increased further, the female variances again increased as polyspermy lowered average fertilization success. Male and female variances differed only at intermediate densities. At low densities, both sexes may be under selection to increase fertilization success; at intermediate densities, males may compete; and at high densities, both sexes may be under selection to increase success by increasing (males) or decreasing (females) likelihood of fertilization during sexual conflict. Only within a narrow range of densities do patterns of sexual selection mirror those typically noted in internally fertilizing taxa.

Density-Dependent Sexual Selection in External Fertilizers: Variances in Male and Female Fertilization Success along the Continuum from Sperm Limitation to Sexual Conflict in the Sea Urchin Strongylocentrotus franciscanus

Density-Dependent Sexual Selection in External Fertilizers: Variances in Male and Female Fertilization Success along the Continuum from Sperm Limitation to Sexual Conflict in the Sea Urchin Strongylocentrotus franciscanus

DENSITY-DEPENDENT SELECTION ON GAMETE TRAITS IN THREE CONGENERIC SEA URCHINS

Because male distribution and abundance strongly influence female fertilization success, density-dependent selection might act on gamete traits to maximize reproductive success. Intra- and interspecific variation in female fertilization success was investigated in the sea urchins Strongylocentrotus purpuratus, S. franciscanus, and S. droebachiensis. Male and female urchins of each species were induced to spawn within 25-m2 plots. The percentage of eggs fertilized, along with six covariates (male density, male–female distance, number of males, surge velocity, advection, and water depth), was measured for each spawning event. S. purpuratus had the highest levels of fertilization (94%), followed by S. franciscanus (64%) and S. droebachiensis (23%). The species with the highest densities, most males, and closest neighbors had the highest levels of fertilization. Depth and surge were not significant factors, but advection was associated with fertilization negatively in S. purpuratus and positively in S. droebachiensis. This interaction is probably caused by the higher degree of clumping in S. purpuratus than in S. droebachiensis. An analysis of covariance indicates that the rank order of least-squares means of percentage fertilization for these three species is the opposite of that for the uncorrected species means. S. droebachiensis performs best and S. purpuratus performs worst, when conditions are held equal. These differences in performance can best be explained by gamete traits. Additional experiments determined (1) that the 25-m2 plot size is the appropriate scale for investigation of patterns of fertilization in S. franciscanus, the species with the largest contiguous populations; (2) that S. purpuratus, the species commonly found in the intertidal and subtidal zones, had similarly high levels of fertilization in the two locations; and (3) that fertilization success in the experimental plots was similar to that during natural spawning events. These results are consistent with density-dependent selection on gamete traits. Gametes of the species that naturally occurs at the lowest population density and has the lowest natural fertilization rates have attributes that cause them to perform the best of the three under conditions of sperm limitation, and those of the species that occurs at the highest densities and has the highest levels of natural fertilization perform most efficiently under conditions of sperm competition. Historical demographic conditions appear to have resulted in selection on gamete traits to maximize reproductive success under conditions of either sperm limitation or sperm competition.

FEMALE RESISTANCE AND MATING OUTCOMES IN A STREAM-DWELLING ISOPOD: EFFECTS OF MALE ENERGY RESERVES AND MATING HISTORY

Abstract In the stream-dwelling isopod, Lirceus fontinalis, conspicuous mating contests occur between males and females prior to pair formation. Our previous work has shown that female resistance during contests determines contest outcomes. Here we examined whether female resistance could act as a mechanism of choice in which females discriminate against males with low energy (glycogen) reserves. We manipulated male glycogen levels by chasing males around a race-track then exposed females to males that differed in glycogen levels. We found that high-glycogen males were more successful than low-glycogen males and that this effect appeared to be due to increased female resistance towards low-glycogen males. We then examined one potential benefit to females of energy-based mate discrimination. In L. fontinalis, male mating history and levels of glycogen reserves are correlated, i.e. recently mated males are glycogen-depleted due to energy costs associated with mating. We examined whether recently mated males were also costly mates, and thus should be avoided by females. We quantified the relationship between male mating history and female fertilization success and found that females suffered an 18% reduction in fertilization success by mating with a male that had recently inseminated another female. We propose that female resistance could act as a mechanism of choice in which males with low energy reserves are avoided and that one benefit of this discrimination is that females increase fertilization success be avoiding males that have recently mated.

Performance of non–motile male gametes in the sea: analysis of paternity and fertilization success in a natural population of a red seaweed, Gracilaria gracilis

In haploid–diploid red seaweeds, the dispersal of male gametes is presumed limited due to their lack of flagella. It has been suggested that this group suffers from sperm limitation and, consequently, that fertilization is relatively inefficient. Fertilization in most floridean rhodophytes results in the formation a cystocarp, a swelling on the haploid female thallus housing the diploid zygote and its thousands of diploid daughter spores. To study the performance of non-motile male gametes in the sea, we evaluated both female and male fertilization success in a natural population of the red marine alga Gracilaria gracilis. Female fertilization success, estimated by cystocarp yield per unit female thallus, was evaluated with respect to the availability of male gametes. Male fertilization success, estimated by the individual contribution of different males to zygotes, was assessed by paternity analyses on 350 cystocarps produced in one reproductive season using two microsatellite loci. The results show that cystocarp yield is not sperm limited and that the large variation in male fertilization success cannot be solely explained by the distance travelled by the male gamete to find a mate. Taken together, the results suggest that, not only is fertilization efficient, but that male–male competition and/or female choice may play a role in shaping population mating patterns.

Fertilization in the sea: are the hazards of broadcast spawning avoided when free–spawned sperm fertilize retained eggs?

In broadcast-spawning marine animals, rapid dilution and short lifespan of sperm following release may impose severely localized patterns of mating. Partial or total failure of external fertilization due to sperm limitation appears commonplace. However, it is not clear to what extent the restrictive kinetics of fertilization in water also constrain mating in animals that release sperm but retain their eggs for fertilization. The compound ascidian Diplosoma listerianum liberates sperm that are dispersed to other colonies and taken in prior to internal cross-fertilization. The fertile lifespan of sperm was found to be long (half-life ca. 8 hours), and a substantial number of fertilizations occurred with 24-hour-old sperm. Fertilizations were obtained from sperm concentrations that would typically produce little or no external fertilization. In a separate experiment, a very small piece of D. listerianum (dry weight less than 2 mg) sired abundant progeny throughout a 3840 l tank. Paternity of progeny in these experiments was confirmed by molecular markers. The same markers were used to extend, to over seven weeks, the known maximum period of storage of exogenous sperm prior to fertilization in this species. The production of only a few thousand sperm at a time by each zooid, poor synchronization of release between zooids, and the existence of many well-spaced exhalant openings in large colonies suggest that D. listerianum is incapable of generating a dense plume of sperm, even close to the source. It is suggested that, unlike external fertilization, successful internal cross-fertilization in D. listerianum is not dependent upon the interception of a dense cloud of gametes just released by a near neighbour. It seems instead that dilute, long-lived sperm can be extracted efficiently from seawater by this suspension feeder, potentially over a period of time. This capability, and other features of the life history, make it unlikely that sperm limitation is an acute problem in this species and comparable taxa, a conclusion with potential significance for expected patterns of mating, sex allocation and gamete attributes in sessile aquatic invertebrates. Variance in reproductive success between individuals due to differences in fertilization rate may be much lower than in broadcast spawners exhibiting external fertilization.

The effect of variation in population density on male fertilization success in a colonial ascidian

Past investigations of the effect of variation in population density on fertilization processes under field conditions have focused entirely on the consequences for female fertilization success (the proportion of eggs fertilized). In contrast, we explored the effects of population size and density on male fertilization success (proportion of embryos fathered or eggs fertilized by individual males) via an in situ density manipulation that utilized allozyme markers to assay paternity after fertilization had occurred. Male-phase ascidian colonies in high density experimental populations experienced competition for fertilizations, which reduced the ability of a focal male to fertilize eggs brooded by individual female colonies. However, the concomitant increase in the number of females with eggs available to be fertilized offset this decline. Consequently, the overall, population-wide fertilization success of focal males did not vary between density treatments. Although population density did not affect the quantitative fertilization success of male colonies, an increase in the genetic diversity of offspring may nevertheless confer a fitness advantage to both males and females that reproduce in higher density populations.