Mating system affects population performance and extinction risk under environmental challenge

Failure of organisms to adapt to sudden environmental changes may lead to extinction. The type of mating system, by affecting fertility and the strength of sexual selection, may have a major impact on a population's chances to adapt and survive. Here, we use experimental evolution in bulb mites (Rhizoglyphus robini) to examine the effects of the mating system on population performance under environmental change. We demonstrate that populations in which monogamy was enforced suffered a dramatic fitness decline when evolving at an increased temperature, whereas the negative effects of change in a thermal environment were alleviated in polygamous populations. Strikingly, within 17 generations, all monogamous populations experiencing higher temperature went extinct, whereas all polygamous populations survived. Our results show that the mating system may have dramatic effects on the risk of extinction under environmental change

Relative costs and benefits of alternative reproductive phenotypes at different temperatures : genotype-by-environment interactions in a sexually selected trait

Abstract Background The maintenance of considerable genetic variation in sexually selected traits (SSTs) is puzzling given directional selection expected to act on these traits. A possible explanation is the existence of a genotype-by-environment (GxE) interaction for fitness, by which elaborate SSTs are favored in some environments but selected against in others. In the current study, we look for such interactions for fitness-related traits in the bulb mite, a male-dimorphic species with discontinuous expression of a heritable SST in the form of enlarged legs that are used as weapons. Results We show that evolution at 18 °C resulted in populations with a higher prevalence of this SST compared to evolution at 24 °C. We further demonstrate that temperature modified male reproductive success in a way that was consistent with these changes. There was a genotype-by-environment interaction for reproductive success – at 18 °C the relative reproductive success of armored males competing with unarmored ones was higher than at the moderate temperature of 24 °C. However, male morph did not have interactive effects with temperature with respect to other life history traits (development time and longevity). Conclusions A male genotype that is associated with the expression of a SST interacted with temperature in determining male reproductive success. This interaction caused an elaborate SST to evolve in different directions (more or less prevalent) depending on the thermal environment. The implication of this finding is that seasonal temperature fluctuations have the potential to maintain male polymorphism within populations. Furthermore, spatial heterogeneity in thermal conditions may cause differences among populations in SST selection. This could potentially cause selection against male immigrants from populations in different environments and thus strengthen barriers to gene flow

No evidence for reproductive isolation through sexual conflict in the bulb mite Rhizoglyphus robini

Sexual conflict leading to sexual antagonistic coevolution has been hypothesized to drive reproductive isolation in allopatric populations and hence lead to speciation. However, the generality of this speciation mechanism is under debate. We used experimental evolution in the bulb mite Rhizoglyphus robini to investigate whether sexual conflict promotes reproductive isolation measured comprehensively to include all possible pre- and post-zygotic mechanisms. We established replicate populations in which we either enforced monogamy, and hence removed sexual conflict by making male and female evolutionary interests congruent, or allowed promiscuity. After 35 and 45 generations of experimental evolution, we found no evidence of reproductive isolation between the populations in any of the mating systems. Our results indicate that sexual conflict does not necessarily drive fast reproductive isolation and it may not be a ubiquitous mechanism leading to speciation

The effect o mutation on eyespan in fly Teleopsis dalmanni.

Female preferences for specific male phenotypes have been observed in many species, yet the mechanisms responsible for the evolution of such preferences still remain to be satisfactorily explained. One of the fundamental unresolved issues is so called lek paradox: directional female choice should deplete genetic variation in male sexually selected traits; however, variation persists. Genic capture hypothesis provides a theoretical resolution to this problem. The hypothesis assumes that the expression of sexual traits largely depends on condition, understood as a pool of resources available for competing life history traits. Condition depends on numerous loci and hence presents a large target for mutations. Genic capture could explain why strong, directional sexual selection does not decrease genetic variation in male sexually selected traits. In accord with the predictions of genic capture hypothesis, male sexual traits should decrease with increasing mutation load more than non-sexual traits. They could therefore signal male genetic quality. Here I investigated the effects of mutations (induced by ionising radiation) on sexual ornament (male eyespan) in stalk- eyed fly Teleopsis dalmanni (Diopsidae). For comparison, I also measured the effects of mutations on non-sexual traits (female eyespan, wing and tibia lenght in both sexes). Neither male eyespan, nor other traits showed significant decrease with increasing mutation load. In contrast to the predictions of genic capture hypothesis, male eyespan did not decrease under mutation load more than non-sexual traits. My results do not support genic capture hypothesis. This indicates that other mechanisms are probably responsible for the maintenance of genetic variation in male eyespan.Ewolucja cech epigamicznych samców i preferencji samic wobec takich cech jest jednym z wciąż nie rozwiązanych problemów biologii ewolucyjnej. Jednym z kluczowych problemów jest rozwiązanie tzw. „paradoksu tokowiska” polegającego na tym, że pomimo silnej preferencji samic wobec jakiejś cechy samców, zmienność w jej obrębie się nie wyczerpuje. Teoretycznym rozwiązaniem „paradoksu tokowiska” jest hipoteza „genic capture” zakładająca, że zmienność w obrębie cech ornamentowych jest utrzymywana dzięki ich zależności od kondycji, rozumianej jako ilość zasobów zgromadzonych i możliwych do wykorzystania przez organizm. Ponieważ kondycja zależy od wielu genów, stanowi ona duży cel dla mutacji, i to może być powodem dla którego silny dobór kierunkowy nie eliminuje zmienności w jej obrębie. Z tego wynika, że cechy ornamentowe mogą być uczciwym sygnałem ogólnogenomowej jakości genetycznej samca i pod wpływem obciążenia mutacyjnego zmniejszać się bardziej niż inne cechy. W niniejszej pracy podjęto próbę przetestowania hipotezy „genic capture”. W tym celu zbadano wpływ mutacji indukowanych promieniowaniem jonizującym na tyczki oczne muchy Teleopsis dalmanni (Diopsidae). Dla porównania mierzono również cechy nie będące pod działaniem doboru płciowego (tyczki oczne samic, długość skrzydła i uda obu płci). Nie udało się wykazać silniejszego wpływu mutacji na tyczki oczne samców niż na inne cechy. Żadna z mierzonych cech nie zmieniła się po wpływem obciążenia mutacyjnego. Uzyskane wyniki nie dostarczyły dowodów na poparcie hipotezy „genic capture” i przemawiają za działaniem innego mechanizmu ewolucji i utrzymywania się cech ornamentowych u tego gatunku

Experimental evolution reveals balancing selection underlying coexistence of alternative male reproductive phenotypes

Heritable alternative reproductive phenotypes (ARPs), which differ in traits associated with competition for mates, occur across taxa. If polymorphism in the genes underlying ARPs is maintained by balancing selection, selection should return ARP proportions to their equilibrium if that equilibrium is perturbed. Here, we used an experimental evolution approach to directly test this prediction in male Rhizoglyphus robini, in which two heritable morphs occur: armored fighters and more female-like, benign scramblers. Using selection lines nearly fixed for male morph, we constructed replicate populations consisting of 50% or 94% fighters, and allowed them to evolve for 14 generations in two types of environment: simple or spatially complex. We found that in both types of populations, the proportion of fighters converged on values within a narrow range of 0.70-0.83, although the rate of convergence was slower in the complex environment. Our results thus demonstrate balancing selection acting on polymorphism(s) underlying ARPs

Data from: Male-limited secondary sexual trait interacts with environment in determining female fitness

Selection for secondary sexual traits (SSTs) elaboration may increase intralocus sexual conflict over the optimal values of traits expressed from shared genomes. This conflict can reduce female fitness, and the resulting gender load can be exacerbated by environmental stress, with consequences for a population’s ability to adapt to novel environments. However, how the evolution of SSTs interacts with environment in determining female fitness is not well understood. Here, we investigated this question using replicate lines of bulb mites selected for increased or decreased prevalence of a male SST—thickened legs used as weapons. The fitness of females from these lines was measured at a temperature to which the mites were adapted (24°C), as well as at two novel temperatures: 18°C and 28°C. We found the prevalence of the SST interacted with temperature in determining female fecundity. At 28°C, females from populations with high SST prevalence were less fecund than females from populations in which the SST was rare, but the reverse was true at 18°C. Thus, a novel environment does not universally depress female fitness more in populations with a high degree of sexually selected dimorphism. We discuss possible consequences of the interaction we detected for adaptation to novel environments

full_dataset

The number of eggs (fecundity) and fertility (fertile collumn; fertile females are coded with 1 and infertile with 0) of females from scrambler (s) and fighter (f) selected lines (sel) at different temperatures (temp). Line identities are given in lineID collumn

Age, experience and sex : do female bulb mites prefer young mating partners?

In species where advancing sire age is associated with decreased progeny fitness, female resistance to mating with old partners can be expected to evolve. In polyandrous species, such resistance may be contingent on female mating experience: virgins should be relatively indiscriminate to ensure egg fertility, whereas non-virgins can be expected to base their re-mating decisions on the age of their previous versus potential new partners, and ‘trade-up’ if previously mated with old males. Here, we tested these predictions using a promiscuous and relatively long-living bulb mite (Rhizoglyphus robini), in which old sire age is associated with decreased fecundity of daughters. In a fully factorial design, we applied two male treatments, young and old, and three female treatments, virgin, previously mated to an old male and previously mated to a young male. Consistent with earlier studies, we observed a reduced mating success of old males. However, we found no support for attributing this result to female discrimination, as female behavior in response to male mounting attempts was not affected by the age of the suitor, or by its interaction with the age of the female’s previous mate. Interestingly, females were passive during 93% of male mounting attempts observed, suggesting that once they are located by a male, they exert little control over copulation. Old males had lower mate-searching activity and were less efficient in obtaining matings (lower success rate per mounting attempt), suggesting a decreased mate-securing ability because of aging. Overall, our results suggest that in bulb mites, male ability to secure mates declines with age, whereas they do not support the prediction that females actively discriminate against old partners

Evolution of mate guarding under the risk of intrasexual aggression in a mite with alternative mating tactics

Mate-guarding strategies are known to evolve in response to changes in the environment, but little is known about the genetic and plastic components of this source of variation. Here, we investigated how risk associated with aggression shapes postcopulatory association time between mates in the bulb mite, Rhizoglyphus robini, a species in which aggressive, armoured fighters often coexist with unarmoured scramblers. In some populations, scramblers have been reported to prevent females remating by remaining in copula for over 6 h. In this study, we investigated whether mate guarding by scramblers is affected by the presence of aggressive fighters in populations. We investigated whether guarding is riskier in the presence of fighters and found that guarding males were more likely to be attacked. Our data allowed us to determine whether the presence of fighters can affect mate-guarding duration, by comparing guarding duration between populations (both natural and artificially selected). We found that in both types of population, males guarded longer when fighters were absent. Comparisons between lines selected for the presence of fighters, lines selected for the presence of scramblers and their source populations indicated that scrambler morphs evolved prolonged guarding. We also investigated whether males show plasticity and shorten guarding in response to the presence of fighters in a social group. Surprisingly, we found that males in a mixed-morph context copulated significantly longer than males from single-morph groups. Our results demonstrate that mate guarding may evolve in response to the presence or absence of fighters in populations, but males are not able to adjust guarding behaviour to the risk of being attacked by fighters. The study provides insight into the role of genetics and plasticity in guarding strategies