Biased Sex Ratios Research Articles

Plasma 17beta-estradiol and alkali-labile phosphoprotein levels in male and female Tench (Tinca tinca) in the Anzali and Amirkolayeh wetlands

Environmental pollutants are potentiate to disturb biological processes such as metabolism, growth and reproduction of aquatic organisms. These compounds are able to cause gonadal abnormalities, biased sex ratios and alteration in reproductive physiology in fish. The aim of this study was to examine plasma 17β-estradiol (E2) and alkali-labile phosphoprotein (ALP) levels in male and female Tench ( Tinca tinca ) from a polluted (the Anzali Wetland) and a non-polluted environments (the Amirkolayeh Wetland). Samples were collected over the maturation season of Tench between May and June 2017. The results revealed significant difference in mean ALP and E2 between genders in the polluted environment. However, the mean plasma ALP concentrations in male Tench of the polluted environment (39.46±1.02 µg/ml) was 45% of the average recorded in female (86.18±2.25 µg/ml) and was two times higher than the amount measured in males in the non-polluted environment (18.68±0.35 µg/ml). High concentrations of E2, were detected in the male samples from the Anzali Wetland. Mean plasma E2 concentrations for male in the Anzali Wetland was almost two times higher than male in the Amirkolayeh Wetland. The results indicate that the reproductive physiology of Tench was affected by contaminants found in the Anzali Wetland, a highly polluted area.

POLYMORPHISM OF RHYNOCORIS MARGINATUS (FAB.) (HETEROPTERA : RUDUVIIDAE) ON THE BIOLOGY, BIOLOGICAL CONTROL POTENTIAL

ABSTRACT To know the influence of polymorphism of Rhynocoris marginatus (Fab.) on the biology, biological control pontential and molecular profile were recorded in the following partners : N male + N female; N male + S female, N male + NS female, NS male + NS female and S + NS female under laboratory conditions. Offspring produced by the S + NS female partners developed quickly having minimum body weight and size and egg hatching percentage, maximum relative growth rate both in first instars and adults, maximum survival rate (82.5 ± 3.50%), male biased sex ratio (0.23). In general, the predatory rate was increased when the prey deprivation period increased from 24 hrs to 72 hrs, third instars to adults. Molecular analysis studies revealed that the total free amino acid was high in N adult morphs. No unique DNA sequence was observed among the morphs of R. marginatus. Among the polymorphic R. marginatus, N male + N female; N male + S female, N male + NS female, NS male + NS female and S + NS, approaching time was also decreased in the latter instars and adult, the biological control potential is highly observed in 96 hrs starved N+N adults showed minimum approaching time, handling time, and high predatory rate. Among the experimental morphs the weight gain was maximum in N+N and minimum weight gain was observed among the morphs of SNS. Minimum total nymphal developmental period, least body weight, survival rate were recorded among the offsprings produced by S+NS, NS+NS and N+NS partners.

Parental sex allocation and sex-specific survival drive offspring sex ratio bias in little owls

Although biased offspring sex ratios are common in species with sexual size dimorphism, the proximate causes are often unresolved. This is because two general mechanisms operating in different ways and in various periods of reproduction can lead to the bias: sex-biased survival or parental sex-allocation. We examined nestling sex ratio patterns between hatching and fledging, sexual size dimorphism, and factors affecting nestling survival using growth and survival data of 846 individual little owl Athene noctua nestlings with known sex from 307 broods from Germany, the Netherlands and Denmark. Nestling sex ratio was female-biased, mainly due to a significant female bias in the first-hatched chicks. Females showed a higher body weight than male nestlings at ringing and body weight of nestlings decreased with hatching sequence. Nestling survival was higher in females (Φ = 0.91) than in males (Φ = 0.85), and survival rates were positively related to body mass and negatively to brood size. Although the observed lower survival of males can cause an overall female-biased sex ratio, the sex dimorphism and survival patterns found here are unlikely to explain the conspicuous sex ratio pattern with a female bias in the first-hatched nestlings and the increase in female bias across the season. Thus, these results point towards interacting mechanisms of parental sex allocation strategies and sex-specific survival. As the female bias was allocated to the first rank that is most likely to survive, the female bias will increase under suboptimal breeding conditions. We therefore suggest that under suboptimal ecological conditions, higher investment into females is adaptive in little owls. Biased sex ratios can have severe effects on the social behaviour and population dynamics of endangered species. However, the existence of subtle sex ratio bias is often unknown and its proximate mechanisms and ultimate consequences often remain unclear. Small sample sizes make the detection of subtle effects unlikely and often fail to disentangle diverging mechanisms such as sex-biased survival and parental sex allocation. We used a large dataset of 846 little owl nestlings from 307 broods from three countries to investigate offspring sex ratio patterns, sexual size dimorphism and nestling survival simultaneously. Our findings suggest interacting mechanisms of parental sex allocation strategies and sex-specific survival to drive biased offspring sex ratios in little owls. The context dependence of the sex ratio bias indicates that offspring sex ratio bias in little owls is both, a consequence of—and an adaptation to—suboptimal breeding conditions.

The foraging behaviour of Aphelinus asychis Walker (Hymenoptera: Aphelinidae) and Aphidius ervi (Haliday) (Hymenoptera: Braconidae) on Myzus persicae (Sulzer) (Hemiptera: Aphididae)

Host stage preference, immature survival, sex ratio and mutual interference of Aphelinus asychis and Aphidius ervi on Myzus persicae were investigated under laboratory (25 + 1 °C; 70 + 5% RH; 16 h light/8 h dark photoperiod). There was significant difference between the rates of parasitism by the two parasitoids on different stages of M. persicae. Second and third instar nymphs of M. persicae were the most preferred for parasitism by A. asychis and A. ervi, respectively. The maximum immature survival was highest (84.3% and 87.4%) in second and third instars of the aphid. A female biased sex-ratio was found for both the parasitoids. Nicholson’s model and linear regression were used to determine per capita search efficiency and the interference coefficient, respectively. The per capita parasitism and search efficiency of the parasitoids were observed to decrease with increase in parasitoid density. The study concluded that A. asychis and A. ervi are effective parasitoids of M. persicae and both of these can be mass reared and utilized in augmentative releases for the management of the aphid under greenhouse environments.

Drivers of sex ratio bias in the eastern bongo: lower inbreeding increases the probability of being born male.

Parent sex ratio allocation has consequences for individual fitness, population dynamics, and conservation. Theory predicts that parents should adjust offspring sex ratio when the fitness returns of producing male or female offspring varies. Previous studies have assumed that only mothers are capable of biasing offspring sex ratios, but have neglected fathers, given the expectation of an equal proportion of X- and Y-chromosome-bearing (CBS) sperm in ejaculates due to sex chromosome segregation at meiosis. This assumption has been recently refuted and both paternal fertility and paternal genetic quality have been shown to bias sex ratios. Here, we simultaneously test the relative contribution of paternal, maternal, and individual genetic quality, as measured by inbreeding, on the probability of being born a son or a daughter, using pedigree and lifelong offspring sex ratio data for the eastern bongo ( Tragelaphus eurycerus isaaci). Our models showed first, that surprisingly, as individual inbreeding decreases the probability of being born male increases, second, that paternal genetic effects on sex ratio were stronger than maternal genetic effects (which were absent). Furthermore, paternal effects were opposite in sign to those predicted; father inbreeding increases the probability of having sons. Previous paternal effects have been interpreted as adaptive due to sex-specific inbreeding depression for reproductive traits. We argue that in the eastern bongo, the opposite sign of the paternal effect on sex ratios results from a reversed sex-specific inbreeding depression pattern (present for female but not male reproductive traits). We anticipate that this research will help stimulate research on evolutionary constraints to sex ratios. Finally, the results open a new avenue of research to predict sex ratio allocation in an applied conservation context. Future models of sex ratio allocation should also include the predicted inbreeding level of the offspring and paternal inbreeding levels.

Sex Ratio of Small Hive Beetles: The Role of Pupation and Adult Longevity.

The sex ratio of sexually reproducing animal species tends to be 1:1, which is known as Fisher’s principle. However, differential mortality and intraspecific competition during pupation can result in a biased adult sex ratio in insects. The female-biased sex ratio of small hive beetles (SHBs) is known from both laboratory and field studies, but the underlying reasons are not well understood. Here, we used laboratory mass and individual pupation to test if differential mortality between sexes and/or intraspecific interactions can explain this sex ratio. The data show a significant female-biased adult sex ratio in both mass and individual rearing, even when assuming that all dead individuals were males. Our results therefore suggest that neither differential mortality during pupation nor intraspecific interactions are likely to explain the female-biased sex ratio of freshly emerged adult SHBs. We regard it as more likely that either competition during the larval feeding stage or genetic mechanisms are involved. In addition, we compared our data with previously published data on the sex ratio of both freshly emerged and field-collected SHBs to investigate possible gender differences in adult longevity. The data show a significantly greater female bias in the sex ratio upon emergence, compared to field-collected SHBs, suggesting that adult females have a shorter longevity.

Variable Abundance and Distribution of Wolbachia and Cardinium Endosymbionts in Plant-Parasitic Nematode Field Populations.

The bacterial endosymbiont Wolbachia interacts with different invertebrate hosts, engaging in diverse symbiotic relationships. Wolbachia is often a reproductive parasite in arthropods, but an obligate mutualist in filarial nematodes. Wolbachia was recently discovered in plant-parasitic nematodes, and, is thus far known in just two genera Pratylenchus and Radopholus, yet the symbiont’s function remains unknown. The occurrence of Wolbachia in these economically important plant pests offers an unexplored biocontrol strategy. However, development of Wolbachia-based biocontrol requires an improved understanding of symbiont-host functional interactions and the symbiont’s prevalence among nematode field populations. This study used a molecular-genetic approach to assess the prevalence of a Wolbachia lineage (wPpe) in 32 field populations of Pratylenchus penetrans. Populations were examined from eight different plant species in Washington, Oregon, and California. Nematodes were also screened for the endosymbiotic bacterium Cardinium (cPpe) that was recently shown to co-infect P. penetrans. Results identified wPpe in 9/32 and cPpe in 1/32 of P. penetrans field populations analyzed. No co-infection was observed in field populations. Wolbachia was detected in nematodes from 4/8 plant-hosts examined (raspberry, strawberry, clover, and lily), and in all three states surveyed. Cardinium was detected in nematodes from mint in Washington. In the wPpe-infected P. penetrans populations collected from raspberry, the prevalence of wPpe infection ranged from 11 to 58%. This pattern is unlike that in filarial nematodes where Wolbachia is an obligate mutualist and occurs in 100% of the host. Further analysis of wPpe-infected populations revealed female-skewed sex ratios (up to 96%), with the degree of skew positively correlating with wPpe prevalence. Uninfected nematode populations had approximately equal numbers of males and females. Comparisons of 54 wPpe 16S ribosomal RNA sequences revealed high similarity across the geographic isolates, with 45 of 54 isolates being identical at this locus. The complete absence of wPpe among some populations and low prevalence in others suggest that this endosymbiont is not an obligate mutualist of P. penetrans. The observed sex ratio bias in wPpe-infected nematode populations is similar to that observed in arthropods where Wolbachia acts as a reproductive manipulator, raising the question of a similar role in plant-parasitic nematodes.

Reproductive biology of the armored catfish Neoplecostomus microps in a coastal Atlantic Forest stream, southeastern Brazil

This work aims to analyze reproductive attributes of the species Neoplecostomus microps (Steindachner, 1877), a well-known species of the catfish family Loricariidae but little con - templated in ecological studies. We describe the reproductive behavior of the species and compare the patterns identified in 2 different basins. The specimens (117 males and 102 females), collected in the Macae River, did not present a bias in sex ratio during the year. In the largest length classes, males predominated and attained earlier maturity than females. The length−weight relationship showed positive allometric growth for both sexes. The variation of the gonadosomatic index and frequency of maturation stages indicated a reproductive period of 4 to 6 mo, starting in September and reaching a peak in November. The mean absolute fecundity was 43.83 (SD = 7.62) oocytes, ranging from 32 to 55 oocytes. The frequency distribution of oocyte diameter of mature ovaries revealed 3 clutches, suggesting batch spawning. A prolonged reproductive period, low fecundity, large eggs, possible parental care, and repeated spawns recorded for N. microps suggest a strategy that maximizes parental fitness. The population structure and reproductive characteristics of this species indicate a tendency toward equilibrium. The early maturation in females in the Macae River population may favor a more rapid replacement of juveniles in the population as a response to the unstable environmental conditions that the population experiences in the rainy season.

Sexual differences in growth and defence of Populus yunnanensis under drought stress

Dioecious woody species often exhibit male-biased sex ratios under drought habitat, which may result in vulnerability in drying soils. However, whether biased sex ratios are associated with sex-specific responses in growth and defence against insect herbivory under drought stress conditions is unknown. We investigated the sexual responses in terms of growth and defence in Populus yunnanensis Dode in response to two water treatments (40% and 100% field capacity). Drought stress reduced the plant growth (e.g., height increment, gas exchange, photosynthetic nitrogen use efficiency, and water potential) of both sexes and reduced the leaf water content and defensive performance (increased damaged area by leaf-chewing generalists and decreased leaf contents of total phenolics, condensed tannins, and flavonoids) of the females but not the males. Moreover, female defensive performance was lower than that of the males under drought conditions. Additionally, the plant mortality rate increased for both sexes, and it was higher for females than for males during drought stress in response to all leaf defoliation treatments. Our results suggest that sexual responses in terms of growth and defence to drought are significantly different and that P. yunnanensis females have a lower defence capability than males, which may explain the male-biased sex ratio that exists in the natural population. Hence, this study provides new insight into forecasting population dynamics for dioecious plant species in drying habitats.

Inbred zebrafish lines: A genetic repository for zebrafish researchers

Genetically uniform strains/inbred strains of animals are used in experiments that demand minimal genetic background variability and highly reproducible results. Modern genomic research is heavily dependent on inbred strains and they are widely used for identification of quantitative loci that affect evolutionarily and biomedically important traits, dissection of gene-gene and gene environmental interaction patterns, toxicity studies, immunology, reverse genetics, cancer research, etc. In mice, over 450 inbred strains have been described and in medaka over 13 inbred strains have been established. Owing to its numerous attributes zebrafish, Danio rerio, is one of the widely studied vertebrate model organisms, but comparable zebrafish inbred strains are not available to the scientific community. This is because of early onset of inbreeding depression causing high mortality of embryos and larvae and biased sex ratio that have been reported from earlier attempts to produce inbred lines. At CZeBraG-Centre for Zebrafish Breeding and Genetics Research facility of ICARCIFE, the inbred lines of zebrafish are being developed. The strategy followed is intense inbreeding coupled with strong positive selection for selected traits. The base population consisted of three wild stocks of zebrafish collected from rivers of North East India. Using nested mating design 84 families were produced in F1 generation and 46 inbred families were produced in F2 generation. Genetic parameters for growth traits like body weight and standard length were estimated. The overall heritability for body weight and standard length was estimated using animal model and found to be 0.43 ± 0.05 and 0.36 ± 0.04 respectively. Fecundity was also recorded but showed no significant variation among stocks. Inbreeding depression was studied by comparing the population means for body weight and standard length of F1 and F2 generation. The analysis suggested there was no inbreeding depression. Genetic monitoring of zebrafish is conducted using microsatellite markers. New PCR primers were designed for 20 selected microsatellite loci with high stringency. High Resolution Melting Curve analysis was used for genotyping individual zebrafish. In addition to developing inbred lines the centre is also maintaining the wild zebrafish stocks and has commenced supply of pedigreed zebrafish for researchers. In future zebrafish of known inbred levels (12.5 to 50% and above) can be supplied. Currently, the CZeBraG can house about 10000 adults, with separate facility for holding individual fish.

Male-skewed sex ratio in Myrica esculenta: a dioecious tree species

The population of M. esculenta tends to deviate from the equilibrium of expected 1:1 primary sex ratio predicted by Fisherian theory. Populations of dioecious plants may often exhibit biased sex ratios, which generally favour males. A study on reproductive potential, i.e., pollen production and female flower production, and reproductive success in Myricaesculenta was assessed in three diameter (diameter at breast height: dbh at 1.37 m) classes, i.e., small (10–20 cm), medium (20–30 cm), and large (30–40 cm). Population structure and sex ratio was determined in transects in four major associations of Myricaesculenta, i.e., (i) with mixed Oak-Rhododendron forest (ii) with Chir Pine–Oak forest, (iii) with pure Oak forest, and (iv) with pure Deodar forest. The sex ratio of trees was male-biased. Male frequency was higher in lower diameter classes and maximum on resource-poor site. More female individuals were recorded in higher-diameter classes and resource rich location, indicating that the total reproductive cost in M. esculenta is greater in female trees than that of the male trees. The population of M.esculenta tends to deviate from the equilibrium of expected 1:1 primary sex ratio predicted by Fisherian theory. The male trees demonstrated greater survival, especially in resource-poor conditions, which was reflected strongly biased sex ratios within the lower size classes. The study would be helpful for formulating appropriate silvicultural and genetic management strategies for this species.

Swift declines predicted following mating system changes driven by an introduced predator.

In Focus: Heinsohn, R., Olah, G., Webb, M., Peakall, R., & Stojanovic, D. (2019). Sex ratio bias and shared paternity reduce individual fitness and population viability in a critically endangered parrot. Journal of Animal Ecology, 88, 502-510. While the effects of variation in the sex ratio of offspring have been thoroughly explored over the last century, the sex ratio of adults has received far less attention. A paper by Heinsohn and colleagues in this issue shows that changes in the adult sex ratio can have striking effects on mating systems, reproductive success and population viability. These impacts are all the more dramatic because they occur in a critically endangered species, the swift parrot, Lathamus discolor, of Tasmania. This species suffers heavy predation from the introduced sugar glider, Petaurus breviceps, which kills nesting females and their clutches, resulting in strongly male-biased adult sex ratios. The authors combined demographic and genetic data to show that, at sites with heavier predation, the remaining females were more likely to mate with multiple males. This shift in the mating system also led to lower overall nesting success, with fewer chicks fledged per nest at sites with higher levels of mixed paternity. Population viability models based on these data predicted steep population declines, with models using the highest observed rates of mixed paternity showing the sharpest declines. These results demonstrate that changes in the adult sex ratio can have far-reaching impacts, including on the fitness of populations themselves.

Sexual conflict in action: An antagonistic relationship between maternal and paternal sex allocation in the tammar wallaby, Notamacropus eugenii.

Sex ratio biases are often inconsistent, both among and within species and populations. While some of these inconsistencies may be due to experimental design, much of the variation remains inexplicable. Recent research suggests that an exclusive focus on mothers may account for some of the inconsistency, with an increasing number of studies showing variation in sperm sex ratios and seminal fluids. Using fluorescent in‐situ hybridization, we show a significant population‐level Y‐chromosome bias in the spermatozoa of wild tammar wallabies, but with significant intraindividual variation between males. We also show a population‐level birth sex ratio trend in the same direction toward male offspring, but a weaning sex ratio that is significantly female‐biased, indicating that males are disproportionately lost during lactation. We hypothesize that sexual conflict between parents may cause mothers to adjust offspring sex ratios after birth, through abandonment of male pouch young and reactivation of diapaused embryos. Further research is required in a captive, controlled setting to understand what is driving and mechanistically controlling sperm sex ratio and offspring sex ratio biases and to understand the sexually antagonistic relationship between mothers and fathers over offspring sex. These results extend beyond sex allocation, as they question studies of population processes that assume equal input of sex chromosomes from fathers, and will also assist with future reproduction studies for management and conservation of marsupials.

Plasticity of Mating Duration in Response to Slightly Biased Operational Sex Ratios in the Water Strider (Aquarius remigis): The Effect of Cohabitation Under Standard Laboratory Conditions

In polygynandrous species, males face the trade-off between the pursuit of increased mating opportunities and securing paternity. Within such systems, males need to accurately assess the social composition of the local environment to maximize fitness. Here, we investigated this capability in the water strider (Aquarius remigis), a semi-aquatic insect known to exhibit a broad spectrum of mating behaviors and inhabit a socially diverse and changing environment. Using a combination of methodological designs to track both within- and between-subject effects, individuals remained in same-sex housing prior to being exposed to slightly biased operational sex ratios (2:1 vs. 1:2) with or without prior cohabitation to determine the effects on mating duration. Results show that males were sensitive to these subtle differences in social conditions, mating for longer periods within male-biased environments, but this was true only under conditions with prior cohabitation. In particular, when individuals could acclimate to the testing environment, mating duration dropped precipitously in female-biased conditions. These findings do not support the view that male water striders have consistent behavioral syndromes, and instead show that individuals are able to differentiate between, and adaptively respond to, small changes in the local sex ratio. In addition to improving our understanding of the plasticity of male mating behavior in this species, this study offers new insights for future laboratory research studying reproductive competition across a diverse range of polygynandrous animals.

Evaluating reasons for biased sex ratios in Crustacea

ABSTRACTWhile equal ratios of males and females are normal, crustacean sex ratios are frequently biased. Here I review potential reasons for sex ratio biases in animals, and evaluate how likely they apply to crustaceans. I introduce crustacean examples and highlight promising crustacean taxa for future studies where examples are lacking. I conclude that ecological differences between the sexes appear to be the dominant reason for sex ratio bias in crustaceans. Major life history patterns limit the importance of evolutionary drivers to sedentary taxa with limited dispersal. Still largely unresolved is the question whether females can bias their offspring sex ratio, and given the diversity of sex determining systems, answers will vary from case to case.Abbreviations: LMC: local mate competition; LSC: local sperm competition.

Manipulated sex ratios alter group structure and cooperation in the brown-headed nuthatch

Abstract A biased adult sex ratio (ASR) can influence cooperative breeding behavior if the bias limits mating opportunities for the more abundant sex. We tested predictions associated with the ASR-cooperation hypothesis in the brown-headed nuthatch (Sitta pusilla). We manipulated ASR by cross-fostering known-sex nestlings within 2 large (≥100 ha) experimental plots for 5 years using a crossover design where each plot received an opposing male- or female-biased treatment for 2 consecutive years. A year with no manipulations followed before the bias was reversed on each plot for 2 additional years. Variation in ASR (adult males/total adults) was pronounced compared to background proportions (0.55) and ranged from a female bias in female-biased plots (0.47) to a strong male bias in male-biased plots (0.71). Sex ratios during the postbreeding period ranged more broadly (0.33 in female-biased plots vs. 0.74 in male-biased plots). Territory densities did not change significantly and allowed 6 predictions to be assessed. Consistent with predictions, the prevalence of cooperative breeding groups doubled under male-biased treatments and large cooperative groups appeared (≥2 male helpers vs. the single male helper most common prior to the experiment). These changes occurred despite increased dispersal of cross-fostered males in male-biased plots. Most juvenile females dispersed, but, consistent with predictions, the prevalence of female helpers increased under female-biased treatments. Manipulations did not alter the sex of nestlings produced nor extend the time that males served as helpers. Taken collectively, results support the ASR-cooperation hypothesis and the role that mate limitations play in cooperative breeding behavior.

Experimental evolution reveals divergence in female genital teeth morphology in response to sexual conflict intensity in a moth.

The rapid evolutionary divergence of male genital structures under sexual selection is well documented. However, variation in female genital traits and the potential for sexual conflict to drive the coevolution between male and female traits has only recently received attention. In many lepidopterans, females possess genital teeth (collectively, signa). Comparative studies suggest these teeth, involved in the deflation of spermatophores, may have coevolved with male spermatophore thickness via sexually antagonistic coevolution in a contest over the rate of deflation of spermatophores within the reproductive tract. We tested the hypothesis that sexual conflict should generate coevolution between genital teeth and spermatophore morphology by examining these traits under experimental manipulation of sexual conflict intensity. Using micro-CT scanning, we examined spermatophore and teeth morphology in populations of the Indian moth, Plodia interpunctella, which had been evolving for 110 generations under different adult sex-ratio biases. We found divergence in female signa morphology in response to sexual conflict: females from female-biased populations (reduced sexual conflict) developed wider signa. However, we found no evidence of coevolution between signa traits and spermatophore thickness as reported from comparative studies.

The proportion of blue light affects parasitoid wasp behavior in LED-extended photoperiod in greenhouses: Increased parasitism and offspring sex ratio bias

The increasing use of specific wavelengths involving light-emitting diodes (LEDs) under greenhouses enables to overcome the lack of light during winter months, helping crops photosynthesis or vegetative growth. However, modification of the light environment as well as the photoperiod may also alter directly or indirectly the activity of both beneficial and pest insects that depend on plants. Here, we submitted the parasitic wasp Aphidius ervi and its main host the pea aphid, to 4 ratios of red(R): blue(B) LEDs used to lengthen the photoperiod inside a growth chamber. We recorded the parasitism rate of aphids and the sex ratio of newly emerged wasps to evaluate if A. ervi could remain an efficient biological control agent under modified light environments. We found that increasing the 8 h of photophase to 16 h by supplementing with R/B LEDs increased the daily parasitic activity of the wasp as well as their egg laying behavior. Under the 100R light supplement, about 80% of the emerged adults were males, against 50% under 25R:75B light treatment. These results indicate that A. ervi remains a good biological control agent when the light environment is modified. However, the use of red light to extend the photophase has the potential to negatively affect population dynamics of these parasitoids due to its male-bias impact on the sex ratio.

The spatial ecology of sex ratios in a dioecious plant: Relations between ramet and genet sex ratios

Abstract In clonal dioecious plants, the frequency and spatial distribution of flowering ramets contains information on the underlying genet sex ratio. These measures can also provide insight on potential ecological mechanisms causing variation and bias in sex ratios among populations. We used a novel likelihood‐based approach and spatial clustering model to estimate the genet sex ratios from flowering ramet data collected from 32 populations of dioecious Thalictrum pubescens, a clonal species from eastern N. America that occupies moist wetland and forested environments. We investigated sex ratios of seed families, clone size, patterns of flowering and plant height to determine potential causes of sex‐ratio bias. Flowering ramet sex ratios varied considerably among populations but were significantly male‐biased. Seed families grown to flowering also exhibited the same degree of male bias. Both models predicted close correspondence between ramet and genet sex ratios. The likelihood model revealed that sex differences in ramet production could not account for biased ramet sex ratios. The spatial clustering model indicated that ramets were significantly clustered at two spatial scales and estimated similar cluster sizes and densities for both sexes. There was no evidence for spatial segregation of the sexes. Both sexes were equally likely to flower in consecutive years and repeated bouts of flowering had no effect on ramet height. Synthesis. Our analyses suggest that the widespread occurrence of male‐biased sex ratios in Thalictrum pubescens is unlikely to result from sexual differences in clonal growth or habitat preferences. The bias appears to become established early in the life cycle, perhaps at the seed stage as a consequence of local resource competition.

Dual social structures in harem-like colony groups of the coral-dwelling damselfish Dascyllus reticulatus depending on body size and sheltering coral structures

The coral-dwelling damselfish Dascyllus reticulatus shows heterosexual cohabitation on branching corals and has been considered to maintain a haremic mating system, where a few males monopolize mating within the group. However, details of the group structure have not been investigated. To clarify the individual-level group structure of D. reticulatus, we conducted field observational surveys on a damselfish population on reefs of Kuchierabu-jima Island, southern Japan. Relatively large D. reticulatus inhabited corals with long branches and wide gaps with a female-biased sex ratio, and they maintained haremic groups where the largest male monopolized mating. In contrast, small adults and juveniles cohabited in higher individual densities on short-branch corals, with no bias in individual sex ratio. Only nine of 26 adult males in the short-branch coral groups showed mating activities. Nineteen of 37 adult females in the short-branch coral groups spawned, and their spawning frequency was lower than that of the females on the long-branch coral. Thus, we observed two contrasting social compositions and mating activities within harem-like cohabitation groups that depended on body size and sheltering coral structures. We observed inter-harem moves by large non-breeding individuals from the short-branch corals to the long-branch corals, implying a conditional use of the two types of groups related to body size. Our observations present a new example of multiple forms of groups in haremic reef fishes.