Balancing Selection, Inversion Polymorphism and Adaptation in Ddt-Resistant Populations of DROSOPHILA MELANOGASTER

The modes of selection important in maintaining an inversion-allozyme polymorphism in two laboratory populations of Drosophila melanogaster were examined. The populations, 731R and J2, are highly resistant to DDT. The polymorphism involves the Standard and In(3R)P chromosomal arrangements in very strong linkage association with the AO ¹ and AO⁴ allozymes, respectively, of the aldehyde oxidase locus—The mean fertilities of the three karyotypes were not significantly different in 731R, but, in J2, In/In was significantly inferior to St/St and St/In. Egg-to-adult viability tests indicated very strong heterozygote advantage at all frequency combinations of the karyotypes in both populations when DDT was present. When DDT was excluded, the viabilities varied over the frequency combinations but were not inversely correlated with karyotype frequency, as predicted by balancing frequency-dependent selection. Discrete, multiple-generation experiments showed a rapid increase in heterozygote frequency to about 80% in both populations when DDT was present. Without DDT, 731R showed apparent directional selection favoring St, whereas J2 showed persistence of the polymorphism, although with extensive fluctuation.—Thus, the inversion-allozyme polymorphism is directly involved in the adaptation to a specific environmental component, DDT, and the selective advantage of the heterozygotes is the important balancing force. Balancing frequency-dependent selection was not observed, which suggests the hypothesis that this form of selection may not be involved in adaptation to novel environmental conditions.     

Does catch and release affect the mating system and individual reproductive success of wild Atlantic salmon (Salmo salar L.)?

In this study, we documented the breeding system of a wild population of Atlantic salmon (Salmo salar L.) by genetically sampling every returning adult and assessed the determinants of individual fitness. We then quantified the impacts of catch and release (C&R) on mating and reproductive success. Both sexes showed high variance in individual reproductive success, and the estimated standardized variance was higher for males (2.86) than for females (0.73). We found a weak positive relationship between body size and fitness and observed that fitness was positively correlated with the number of mates, especially in males. Mature male parr sired 44% of the analysed offspring. The impact of C&R on the number of offspring was size dependent, as the reproductive success of larger fish was more impaired than smaller ones. Also, there was an interactive negative effect of water temperature and air exposure time on reproductive success of C&R salmon. This study improves our understanding of the complex reproductive biology of the Atlantic salmon and is the first to investigate the impact of C&R on reproductive success. Our study expands the management toolbox of appropriate C&R practices that promote conservation of salmon populations and limit negative impacts on mating and reproductive success.     

SELECTION AND THE “SEX-RATIO” POLYMORPHISM IN NATURAL POPULATIONS OF DROSOPHILA PSEUDOOBSCURA

“Sex-ratio” (SR) is a naturally occurring X-linked meiotic drive system, where the SR-X chromosome is transmitted to nearly all progeny of SR males. It occurs at frequencies of up to 25% in some populations of Drosophila pseudoobscura. Because of the twofold drive advantage, SR should rapidly fix in populations, causing the extinction of the species, unless opposed by strong selection. I examine several of the adult components of fitness, including the frequencies of all genotypic mating combinations, fertilities, and fecundities of flies from two populations in southeastern Arizona. Significant reduction of fecundity of SR/SR females was observed in the Tucson population. No evidence was found for either lower fertility or reduced mating success of SR males, relative to standard males. Most selection opposing SR appears to be operating at the larval stages in nature.     

Sex‐specific selection and sexual size dimorphism in the waterstrider Aquarius remigis

We estimated selection on adult body size for two generations in two populations of Aquarius remigis, as part of a long‐term study of the adaptive significance of sexual size dimorphism (SSD). Net adult fitness was estimated from the following components: prereproductive survival, daily reproductive success (mating frequency or fecundity), and reproductive lifespan. Standardized selection gradients were estimated for total length and for thorax, abdomen, genital and mesofemur lengths. Although selection was generally weak and showed significant temporal and spatial heterogeneity, patterns were consistent with SSD. Prereproductive survival was strongly influenced by date of eclosion, but size (thorax and genital lengths in females; total and abdomen lengths in males) played a significant secondary role. Sexual selection favoured smaller males with longer external genitalia in one population. Net adult fitness was not significantly related to body size in females, but was negatively related to size (thorax and total length) in males.     

Genetic evidence for the mating system and reproductive success of black sea bream (Acanthopagrus schlegelii)

Understanding the mating system and reproductive success of a species provides evidence for sexual selection. We examined the mating system and the reproductive success of captive adult black sea bream (Acanthopagrus schlegelii), using parentage assignment based on two microsatellites multiplex PCR systems, with 91.5% accuracy in a mixed family (29 sires, 25 dams, and 200 offspring). Based on the parentage result, we found that 93.1% of males and 100% of females participated in reproduction. A total of 79% of males and 92% of females mated with multiple partners (only 1 sire and 1 dam were monogamous), indicating that polygynandry best described the genetic mating system of black sea bream. For males, maximizing the reproductive success by multiple mating was accorded with the sexual selection theory while the material benefits hypothesis may contribute to explain the multiple mating for females. For both sexes, there was a significant correlation between mating success and reproductive success and the variance in reproductive success of males was higher than females. Variation in mating success is the greatest determinant to variation in reproductive success when the relationship is strongly positive. The opportunity for sexual selection of males was twice that of females, as well as the higher slope of the Bateman curve in males suggested that the intensity of intrasexual selection of males was higher than females. Thus, male–male competition would lead to the greater variation of mating success for males, which caused greater variation in reproductive success in males. The effective population number of breeders (N_b) was 33, and the N_b/N ratio was 0.61, slightly higher than the general ratio in polygynandrous fish populations which possibly because most individuals mated and had offspring with a low variance. The relatively high N_b contributes to the maintenance of genetic diversity in farmed black sea bream populations.     

Functional infertility in a wild passerine bird

Information about male infertility in free‐living bird populations and its underlying causes are poorly documented in the literature. Here, we assessed sperm quality and infertility among males in a wild population of Blue Tits Cyanistes caeruleus, a socially monogamous passerine with frequent extra‐pair mating. One of 30 males (3.3%) studied across two breeding seasons had morphologically abnormal and nearly immotile spermatozoa in combination with zero annual fertilization success. Demonstration of male functional infertility suggests the possibility that socially monogamous females of the study population could obtain a direct fitness benefit by mating polyandrously to increase fertilization success, which could contribute to selection on extra‐pair mating behaviour.     

Testing for local adaptation in adult male and female fitness among populations evolved under different mate competition regimes

Mating/fertilization success and fecundity are influenced by sexual interactions among individuals, the nature and frequency of which can vary among different environments. The extent of local adaptation for such adult fitness components is poorly understood. We allowed 63 populations of Drosophila melanogaster to independently evolve in one of three mating environments that alter sexual interactions: one involved enforced monogamy, while the other two permitted polygamy in either structurally simple standard fly vials or in larger “cages” with added complexity. Adult male and female reproductive fitness were measured after 16 and 28 generations, respectively, via full reciprocal transplants. In males, reciprocal local adaptation was observed between the monogamy and simple polygamy treatments, consistent with the evolution of reproductively competitive males under polygamy that perform poorly under monogamy because they harm their only mate. However, males evolved in the complex polygamy treatment performed similarly or better than all other males in all mating environments, consistent with previous results showing higher genetic quality in this treatment. Differences in female fitness were more muted, suggesting selection on females was less divergent across the mating treatments and echoing a common pattern of greater phenotypic and expression divergence in males than females.     

Inbreeding Depression and Inbreeding Avoidance in a Natural Population of Guppies (Poecilia reticulata)

Maintenance of genetic variation in the face of strong natural selection is a long‐standing problem in evolutionary biology. One of the most extreme examples of within‐population variation is the polymorphic, genetically determined color pattern of male Trinidad guppies (Poecilia reticulata). Female mating preference for rare or novel patterns has been implicated as a factor in maintaining this variation. The origin of this preference is not understood, although inbreeding avoidance has been proposed as a mechanism. Inbreeding avoidance is advantageous when populations exhibit inbreeding depression and the opportunity for mating between relatives exists. To determine whether these conditions are met in a natural guppy population, we assessed mating and reproductive patterns using polymorphic molecular markers. Females produced more offspring with less‐related males than with more‐related ones. In addition, females were more likely to have mated with less‐related males, but this trend was only marginally significant. Male heterozygosity was positively correlated with mating success and with the number of offspring sired, consistent with strong inbreeding depression for adult male fitness. These results provide substantial insight into mating patterns of a wild guppy population: strong inbreeding depression occurs, and individuals tend to avoid mating with relatives.     

Intergenerational paternal effect of adult density in Drosophila melanogaster

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Influence of male mating history on female reproductive success among monandrous Naryciinae (Lepidoptera: Psychidae)

1. Multiple male copulations can have detrimental effects on female fitness due to sperm limitation. 2. Monandrous Naryciinae females are immobile while the males are short‐lived and do not feed. Multiple male mating is therefore expected to lead to sperm limitation in females. Sperm limitation and male limitation are hypothesised as causes of the repeated evolution of parthenogenetic reproduction in the Psychidae. 3. In this study, the effects of multiple male mating on female reproduction are investigated in several species of Naryciinae by allowing males multiple copulations. The results for two species, Siederia listerella and Dahlica lichenella, are compared. The sex ratios of 53 natural populations are examined for indications of male limitation. 4. Previous copulations by the male increased the female's risk of remaining unfertilised. However, contrary to expectations, those unfertilised females were capable of successful re‐mating. 5. In S. listerella, the number of previous copulations of males negatively influenced female fitness. Females produced 30% fewer offspring if they mated with a previously mated male. In D. lichenella, the older the male and the lower its number of total lifetime copulations, the higher the female's reproductive success. 6. Only a fraction of the investigated populations had a female‐skewed sex ratio, but differences in development time between males and females could lead to reproductive asynchrony. 7. In conclusion, male mating history did not lead to strong sperm limitation in Naryciinae as had been suggested by their life history.     

Mating behaviour of the ‘cosmopolitan’ species Phyllognathopus viguieri (Copepoda: Harpacticoida) and its systematical significance

The mating behaviour was studied and recorded on video with individuals of four cultures of Phyllognathopus viguieri from different populations obtained from the interstitial water of a slow sand filter near the river Ruhr (Germany) (Ruhr population), from a compost heap in Bethesda (Maryland, USA) (Maryland population), from a rain gauge in Windsor Campbell farm (Jamaica) (Jamaica population), and a tree trunk with moss in a forest in the municipality of Rio de Janeiro (Brazil) (Brazil population). The mating behaviour was divided into the well‐known initial phase, copula phase and postcopulatory mate guarding phase. An additional phase prior to the initial phase serves to recognize the female, the recognition phase. The mating behaviour is identical in the males of the Jamaica and Brazil populations of P. viguieri. A postcopulatory mate guarding phase is not found in these two groups. Here, we refute the hypothesis, that a postcopulatory mate guarding phase is found in taxa in which only adult males grasp adult females. The males of the Ruhr and Maryland populations differ from each other in their mating behaviour. Generally, the males of all four populations do not mate with fertilized females which are equally unattractive to the males, i.e., females mate only once in their lifetime to produce offspring. These results corroborate the view that the different populations of P. viguieri do not belong to a single cosmopolitan species.     

Males from populations with higher competitive mating success produce sons with lower fitness

Female mate choice can result in direct benefits to the female or indirect benefits through her offspring. Females can increase their fitness by mating with males whose genes encode increased survivorship and reproductive output. Alternatively, male investment in enhanced mating success may come at the cost of reduced investment in offspring fitness. Here, we measure male mating success in a mating arena that allows for male–male, male–female and female–female interactions in Drosophila melanogaster. We then use isofemale line population measurements to correlate male mating success with sperm competitive ability, the number of offspring produced and the indirect benefits of the number of offspring produced by daughters and sons. We find that males from populations that gain more copulations do not increase female fitness through increased offspring production, nor do these males fare better in sperm competition. Instead, we find that these populations have a reduced reproductive output of sons, indicating a potential reproductive trade‐off between male mating success and offspring quality.     

Spatial Segregation of the Sexes and Nutrients affect Reproductive Success in a Dioecious Wind-pollinated Grass

In many dioecious plant species in which spatial distributions of males and females have been examined, the sexes are spatially segregated – usually along an environmental gradient. Unless pollen is uniformly distributed in a population, spatial segregation of the sexes should reduce the average mating success of individuals. In three Californian populations of Distichlis spicata – a wind-pollinated grass species that exhibits spatial segregation of the sexes – I examined patterns of pollen movement and the effects of pollen load and nutrient availability on seed set to determine whether spatial segregation of the sexes actually reduces mating success for both males and females. In two of the populations, pollen dispersal was restricted, and pollen augmentation consistently, significantly increased seed set. However, in the third population – which had the lowest seed set – I found that although there were some indications of pollen limitation, pollen dispersal was not restricted, and seed production was limited primarily by nutrient availability. These results imply that in some populations of D. spicata nutrient limitation on the production of seeds by females may be sufficiently strong that spatial segregation of the sexes causes a fairly low cost to reproductive success compared with a more random distribution of the sexes. However, in other populations, pollen does limit mating success, and the spatial segregation of males and females in these populations is reducing the fecundity of both males and females.     

Interspecific Social Interactions and Breeding Success of the Frog Rana latastei: A Field Study

Interspecific reproductive interference can affect fitness‐related breeding performance, thus influencing fitness and distribution of populations. Laboratory studies demonstrated the social interference of Rana dalmatina males on R. latastei breeding females: the presence of heterospecific males reduced the percentage of viable embryos in R. latastei eggs. Here, we tested if the negative effects of R. dalmatina males on R. latastei reproductive success occur in field conditions. We compared the percentage of viable embryos of eggs laid in field conditions from populations where R. latastei breeds alone with the percentage of viable embryos of populations where R. latastei cohabits with R. dalmatina. We did not find any significant difference in percentage of viable embryos between R. latastei populations syntopic and allotopic with R. dalmatina, nor a relationship between the relative abundance of heterospecifics and reproductive success. In natural conditions, the presence of heterospecific males does not seem to interfere with the reproductive success of R. latastei. The experimental procedure may influence the interaction among individuals. Therefore, we suggest to validate on natural populations the results of experiments dealing with complex interactions.     

Male mating success,sexual size dimorphism,and site fidelity in two species of Malacoctenus (Labrisomidae)

Synopsis In both Malacoctenus hubbsi and Malacoctenus macropus, males defended preferred oviposition sites from both other males and potential egg predators. In M. hubbsi, adult females were larger than adult males. Larger M. hubbsi males were not associated with territory parameters that were correlated with higher mating success, and male size was not correlated with mating success. Male size did affect mating success when territory parameters were statistically controlled for, but the failure of large males to associate with better territories eliminated any mating advantage for larger males. In M. macropus, males are larger than females. Larger males defended preferred oviposition sites, and had higher mating success than did smaller males. Male M. macropus also had much higher site fidelity than male M. hubbsi. These results suggest that the evolution of the differences in site fidelity and sexual size dimorphism between these two species may be due to sexual selection acting differentially in these two species.     

Evolution of life‐history traits and mating strategy in males: a case study on two populations of a Drosophila parasitoid

Abiotic and biotic factors affect life‐history traits and lead populations to exhibit different behavioural strategies. Due to the direct link between their behaviour and fitness, parasitoid females have often been used to test the theories explaining these differences. In male parasitoids, however, such investigations are vastly understudied, although their mating strategy directly determines their fitness. In this study, we compared the pattern of life history traits and the mating strategy of males in two populations of the Drosophila parasitoid Asobara tabida, exposed to different biotic and abiotic conditions, with the major difference being that one of them was recently exposed to strong competition with the dominant competitor Leptopilina boulardi after recent climate change, the other population being settled in a location where L. boulardi has not been recorded. The results showed that individuals of both populations have a different reproductive strategy: in one population, females produced a more female‐biased sex ratio, while males accumulated more lipids during their larval development, invested more energy in reproduction and decreased their locomotor activity, suggesting a higher proportion of matings on their emergence patch, all of these factors being possibly linked to the new competition pressure. In both populations, mating without sperm transfer may persist for several days after males become sperm‐depleted, and may be more frequent than mating with sperm transfer over their whole lifespan. This point is discussed from an evolutionary point of view.     

Influence of Male Songs on Female Mating Behavior in the Grasshopper Chorthippus biguttulus (Orthoptera: Acrididae)

In males of the grasshopper Chorthippus biguttulus the relationship between song and mating success was investigated in three isolated field populations of individually marked animals within their natural habitat. In a population with muted males (forewings removed), females mated on average 1.7 days later than in a population with intact males. But approximately 14 days after the imaginal moult, roughly corresponding with the time of the first oviposition, 100% of females in both populations had mated. In a further test population, females with a choice between singing and mute males mated almost exclusively (16 from 17 observed copulations) with the intact, singing males. The chance encounter frequency of a male and female was equally high for all populations (on average one encounter every 1.2 h). Different encounter probabilities cannot therefore have caused either mating delay in the population with muted males or preferential selection of intact partners.     

An integrative mating system assessment of a nonmodel,economically important Pacific rockfish (Sebastes melanops) reveals nonterritorial polygamy and conservation implications for a large species flock

Characterizing the mating systems of long‐lived, economically important Pacific rockfishes comprising the viviparous Sebastes species flock is crucial for their conservation. However, direct assignment of mating success to sires is precluded by open, offshore populations and high female fecundity. We addressed this challenge by integrating paternity‐assigned mating success of females with the adult sex ratio (ASR) of the population, male evolutionary responses to receptive females, and reproductive life history traits—in the framework of sexual selection theory—to assess the mating system of Sebastes melanops. Microsatellite parentage analysis of 17 pregnant females, 1,256 of their progeny, and 106 adults from the population yielded one to four sires per brood, a mean of two sires, and a female mate frequency distribution with a truncated normal (random) pattern. The 11 multiple paternity broods all contained higher median allele richness than the six single paternity broods (Wilcoxon test: W = 0, p < .001), despite similar levels of average heterozygosity. By sampling sperm and alleles from different males, polyandrous females gain opportunities to enhance their sperm supply and to lower the cost of mating with genetically incompatible males through reproductive compensation. A mean of two mates per mated female with a variance of one, an ASR = 1.2 females per male, and the expected population mean of 2.4 mates for mated males (and the estimated 35 unavailable sires), fits polygamous male mate frequency distributions that distinguish polygynandry and polyandrogyny mating systems, that is, variations of polygamy, but not polyandry. Inference for polygamy is consistent with weak premating sexual selection on males, expected in mid‐water, schooling S. melanops, owing to polyandrous mating, moderately aggregated receptive females, an even ASR, and no territories and nests used for reproduction. Each of these characteristics facilitates more mating males and erodes conspicuous sexual dimorphism. Evaluation of male evolutionary responses of demersal congeners that express reproductively territorial behavior revealed they have more potential mechanisms for producing premating sexual selection, greater variation in reproductive success, and a reduced breeding effective population size of adults and annual effective size of a cohort, compared to S. melanops modeled with two mates per adult. Such divergence in behavior and mating system by territorial species may differentially lower their per capita birth rates, subsequent population growth, and slow their recovery from exploitation.     

Time spent in distinct life history stages has sex‐specific effects on reproductive fitness in wild Atlantic salmon

In species with complex life cycles, life history theory predicts that fitness is affected by conditions encountered in previous life history stages. Here, we use a 4‐year pedigree to investigate if time spent in two distinct life history stages has sex‐specific reproductive fitness consequences in anadromous Atlantic salmon (Salmo salar). We determined the amount of years spent in fresh water as juveniles (freshwater age, FW, measured in years), and years spent in the marine environment as adults (sea age, SW, measured in sea winters) on 264 sexually mature adults collected on a river spawning ground. We then estimated reproductive fitness as the number of offspring (reproductive success) and the number of mates (mating success) using genetic parentage analysis (>5,000 offspring). Sea age is significantly and positively correlated with reproductive and mating success of both sexes whereby older and larger individuals gained the highest reproductive fitness benefits (females: 62.2% increase in offspring/SW and 34.8% increase in mate number/SW; males: 201.9% offspring/SW and 60.3% mates/SW). Younger freshwater age was significantly related to older sea age and thus increased reproductive fitness, but only among females (females: ?33.9% offspring/FW and ?32.4% mates/FW). This result implies that females can obtain higher reproductive fitness by transitioning to the marine environment earlier. In contrast, male mating and reproductive success was unaffected by freshwater age and more males returned at a younger age than females despite the reproductive fitness advantage of later sea age maturation. Our results show that the timing of transitions between juvenile and adult phases has a sex‐specific consequence on female reproductive fitness, demonstrating a life history trade‐off between maturation and reproduction in wild Atlantic salmon.     

Effects of multiple matings on reproductive fitness of male and female Diaeretiella rapae

Mating frequency and the amount of sperm transferred during mating have important consequences on progeny sex ratio and fitness of haplodiploid insects. Production of female offspring may be limited by the availability of sperm for fertilizing eggs. This study examined multiple mating and its effect on fitness of the cabbage aphid parasitoid Diaeretiella rapae McIntosh (Hymenoptera: Aphidiidae). Female D. rapae mated once, whereas males mated with on average more than three females in a single day. The minimum time lag between two consecutive matings by a male was 3 min, and the maximum number of matings a male achieved in a day was eight. Sperm depletion occurred as a consequence of multiple mating in D. rapae. The number of daughters produced by females that mated with multiple‐mated males was negatively correlated with the number of matings achieved by these males. Similarly, the proportion of female progeny decreased in females that mated with males that had already mated three times. Although the proportion of female progeny resulting from multiple mating decreased, the decrease was quicker when the mating occurred on the same day than when the matings occurred once per day over several days. Mating success of males initially increased after the first mating, but then males became ‘exhausted’ in later matings; their mating success decreased with the number of prior matings. The fertility of females was affected by mating with multiple‐mated males. The study suggests that male mating history affects the fitness of male and female D. rapae.