Larger Females Research Articles

Disruption of male mating strategies in a chemically compromised environment

A leading source of endocrine-disrupting chemicals (EDCs) in the environment is run-off of veterinary pharmaceuticals used in agriculture, including hormonal growth promotants (HGPs). Despite being banned in various countries, HGP use is still common in beef production around the world. The androgenic steroid 17β-trenbolone (17β-TB) is a HGP that commonly enters surface waters via livestock effluent run-off. Here, we used a flow-through system to expose wild-caught adult male guppies (Poecilia reticulata) to an environmentally realistic level of 17β-TB (average measured concentration = 2 ng/L) for 21 days. We then compared the response of exposed and unexposed males to sequentially presented large and small stimulus (unexposed) females. Due to a positive size-fecundity relationship, larger females are generally expected to be preferred by males. While we found no evidence that the size of a previously encountered female affected the amount of courtship or coercive ‘sneak’ mating behaviour performed by males during the second presentation, males from both exposure treatments conducted more frequent courting events towards larger females during both presentations, suggesting an absolute preference for greater female size. Further, across both presentations, 17β-TB exposure caused a shift in male mating strategy towards increased coercive sneaking behaviour, although male sequential investment into mating effort was not impacted at the tested dosage. In combination, our findings demonstrate that exposure to a field-realistic level of a widespread agricultural pollutant alters male mating strategies in fish, and contribute to a growing understanding of sub-lethal impacts of chemical contaminants on complex behaviours in wildlife.

Body size, but not age‐at‐maturation or context, affects the expression of predator‐induced behavioural plasticity in female green swordtails (Xiphophorus hellerii)

AbstractBehavioural plasticity is a form of reversible phenotypic plasticity in which a genotype can express different behavioural phenotypes under different environmental conditions. Though an interest in among‐individual differences in behavioural plasticity has flourished in recent decades, few studies have considered the effects of intrinsic factors, such as life‐history or morphological traits, in tandem with extrinsic factors, such as presence of conspecifics in different social contexts, on predator‐induced behavioural plasticity. Here, we present a study conducted with female green swordtail fishes, Xiphophorus hellerii, designed to assess the effects of age‐at‐maturation and body size on the expression of predator‐induced behavioural plasticity in two social contexts: (a) female‐only (two females) and (b) female‐and‐male (two females and a male). We further examined the extent to which individual expression of behavioural plasticity is consistent across these two social contexts. We found that in the presence of a predator, focal females were more timid in response to the stimulus and more tolerant of the non‐focal female, and small females expressed this change from bold/less tolerant to timid/more tolerant to a greater degree than large females, regardless of age‐at‐maturation. However, individuals were not consistent in the degree or direction of plasticity expressed in the behaviours of interest between the female‐only and the female‐and‐male context. Here, we show that within‐ and among‐individual differences in behavioural expression are common but inconsistent. How intrinsic and extrinsic factors independently or together drive expression of plasticity in antipredator and agonistic behaviours is varied and warrants further study.

Does meiotic drive alter male mate preference?

AbstractMale mate preferences have been demonstrated across a range of species, including the Malaysian stalk-eyed fly, Teleopsis dalmanni. This species is subject to sex-ratio (SR), an X-linked male meiotic driver, which causes the dysfunction of Y-sperm and the production of all-female broods. While there has been work considering female avoidance of meiotic drive males, the mating decisions of drive-bearing males have not been considered previously. Drive males may be less able to bear the cost of choice as SR is associated with a low-frequency inversion that causes reduced organismal fitness. Drive males may also experience weaker selection for preference maintenance if they are avoided by females. Using binary choice trials, across two experiments, we confirmed male preference for large (fecund) females but found no evidence that the strength of male preference differs between drive and standard males. We showed that large eyespan males displayed strong preference for large females, whereas small eyespan males showed no preference. Taken together, these results suggest that, even though meiotic drive is associated with lower genetic quality, it does not directly interfere with male mate preference among available females. However, as drive males tend to have smaller eyespan (albeit only ~5% on average), this will to a minor extent weaken their strength of preference.

Mesocarnivores affect hispid cotton rat (Sigmodon hispidus) body mass

Predator communities are changing worldwide: large carnivores are declining while mesocarnivores (medium-sized mammalian predators) are increasing in number and ecological influence. Predator choice of prey is not random and different predators select prey with different characteristics. Changes in predator communities can change predation patterns experienced by prey. Little is known about how mesocarnivore communities influence prey morphology. We used 14 years of mark-recapture data to investigate how mesocarnivore exclusion affected body mass of hispid cotton rats (Sigmodon hispidus). Finding adult male cotton rats were 9% heavier with mesocarnivore exclusion, we developed hypotheses to explain this observation. Greater adult male body mass in exclosures resulted from: (1) a non-significant trend of increased survival of large males, (2) faster juvenile male growth during the fall and a similar non-significant trend among adult males, and (3) spatial partitioning by size among males. Taxa-specific predation rates (i.e., rates of predation by snakes, raptors, or mesocarnivores) did not differ among male body mass classes. Mesocarnivores disproportionately preyed on large females while raptors targeted small females, but female body mass was not influenced by mesocarnivore exclusion. Changes in predator communities can result in multiple small effects that collectively result in large differences in prey morphology.

Size‐dependent mating preference of the male fiddler crab Austruca perplexa

AbstractIn many animals, females prefer large males to small males, which allow large males to be choosier than small males when selecting a mate. We investigated the courtship intensity of small‐ and large‐sized male fiddler crabs (Austruca perplexa) by examining their claw‐waving rates (waves/min) towards small‐ and large‐sized females. We found that large males showed a greater preference for large females by producing more waves/min towards them, whereas small males did not show any apparent preference for either large or small females. Moreover, the waving rate of large males was positively correlated with female size, but there was no correlation between waving rate and female size in small males. These results indicate that large males in a population become choosier and show strong mate choice, which is most likely due to their greater preference among females.

Someone like me: Size-assortative pairing and mating in an Amazonian fish, sailfin tetra Crenuchus spilurus

In the absence of constraints, preference for larger mates is expected to evolve, as larger individuals are typical of higher potential fitness. Large females are often more fecund and carry larger eggs (which result in higher number and better quality of offspring), whereas large males usually have more conspicuous ornaments and are better at defending resources. However, intrasexual competition can constrain the access to larger partners, especially when opportunities for mate takeover abound. Here we investigate the relationship between individual’s size and mate choice in relation to one’s own size and their respective mate’s size using the sailfin tetra, a sexually dimorphic Amazonian fish species. We show that ornaments of larger males are exponentially more conspicuous, and larger females are more fecund and carry larger eggs. Contrary to expectation, neither males nor females associated for longer with the larger of two offered potential mates. Instead, individuals of both genders chose opposite-sex individuals of similar sizes to themselves. Additionally, similar-sized pairs were more likely to spawn than couples with higher size asymmetries. Grounded on field observations, we propose that prudent choice should be particularly important in this system, since courtship is long (often taking several days), which offers opportunities for mate takeover. Intrasexual competition, however, cannot readily explain female choice for similar-sized males. We thus suggest that such preference might be best explained by avoidance of filial cannibalism.

Behavior of "Intermediate" Males of the Dimorphic Squid Doryteuthis pleii Supports an Ontogenetic Expression of Alternative Phenotypes.

The expression of alternative reproductive tactics (ARTs) by different-sized males of loliginid squids has been extensively investigated. In loliginids, alternative phenotypes are characterized by discontinuous differences in behavior, body size, sperm deposition site, and morphology and functioning of ejaculates. Large consort males guard females, display agonistic behaviors toward rival consort males, and mate with females in the male-parallel (MP) position. Small sneaker males avoid fighting contests and instead adopt furtive behaviors to access females guarded by consort males, mating with females in the head-to-head (HH) posture. Recently, the reappraisal of preserved material from the loliginid squid Doryteuthis pleii showed that intermediate-sized males (so-called “intermediate” males) had both sneaker- and consort-like ejaculates, leading to the hypothesis of them being a transitional stage between both phenotypes. Here, we describe observations made in captivity showing that intermediate males can display agonistic behaviors toward consort males and mate with females in both mating positions, depending on the male’s current reproductive context, i.e., generally in HH, but switching to MP when the female is laying eggs. Such unusual findings of intermediate males simultaneously displaying behaviors of both sneaker and consort males comprise additional evidence corroborating the ontogenetic hypothesis for phenotypic expression of ARTs in this species. Taken together, our results indicate that (1) instead of competing with large consort males for female access and monopolization, small/young males adopt sneaker tactics to obtain mating opportunities, and (2) as they continue to grow, they gradually modify the morphology of their ejaculates and their mating behavior, going through an “intermediate” stage, before becoming large consort males.

Allometry of reaching and contact structures in Kukulcania hibernalis (Araneae: Filistatidae).

Large part of the morphological diversity observed across taxa is attributed to the effect of sexual selection; and the static allometry of these structures vary largely from highly positive to negative, depending on their function, and position on the animal's body. In arthropods, information of how sexually selected contact and reaching male structures use during courtship scale on body size is scarce. We tested two complementary hypotheses: the reaching structure hypothesis and the contact-function hypothesis, in the spider Kukulcania hibernalis. We used the length of the proximal segments of the male pedipalp to test the reaching structure hypothesis, and claw features to test the contact-function hypothesis. Our results support both hypotheses. Small males have disproportionally longer pedipalps (highly negative allometry) than large males, increasing the probability of small-bodied males to inseminate even large females. We also found that both distal contact and noncontact homologous structures scaled shallow (slope < 1) on body size, but allometry was significantly shallower for contact than for noncontact distal structures, providing support to the contact-function hypothesis, and allowing teasing apart the effect of sexual selection on distal contact structures with dual functions.

Large mothers produce progeny with high survival rates during the immature stage and large sizes at adulthood in a parasitoid species.

Parasitoid researchers have generally thought that the body size of the mother parasitoid does not affect the fitness performance of the progeny during the immature stage, as long as the progeny develop in the same environment. We reveal for the first time that this is not true for the parasitoid Echthrodelphax fairchildii (Hymenoptera: Dryinidae), which is parasitic on planthoppers. Large females ensured an increased survival rate for their progeny during the immature stage and a large body size at adult emergence. Maternal body size differentially affected the body sizes and survival rates of male and female progeny. Small females did not produce female progeny, and the survival rate of the female progeny increased more steeply with increasing maternal body size than that of the male progeny. Meanwhile, the body size of male progeny increased more steeply with increasing maternal body size. The influence of maternal body size on progeny survival to adult emergence has never been reported in insects before. In addition, large females were more likely to lay female eggs, suggesting that females control the sex ratio of progeny in response to their own body size.

Operational sex ratio does not influence the evolution of male mate choice in the Indian meal moth

The strength of mate choice, pre-copulatory sexual selection more generally, is predicted to vary according to a range of social and demographic factors, including the operational sex ratio (OSR). The OSR influences the number of mating opportunities available to each sex, and can, therefore, strongly influence the degree of intrasexual competition and the cost of mate choice. Accordingly, many animals show short-term plasticity in the strength of mate choice in relation to changes in the OSR. However, whether such change persists over evolutionary time has rarely been tested experimentally. In this study, we examined how female mating success in relation to larval food level and body size differs according to the evolutionary history of their mates, in the Indian meal moth Plodia interpunctella. We used males from populations that have been reared at different adult sex ratios (and, therefore, OSRs) for 130 + generations. We found that small females were more likely to mate compared to large females; however, this effect could not be attributed exclusively to male mate choice. Larval food level also did not influence female mating success. Further, males from different sex ratio regimes did not differ in their likelihood of mating with small females, or those from high-food populations. We suggest that male post-copulatory choice is potentially more important than pre-copulatory choice in this species.

Be prudent if it fits you well: male mate choice depends on male size in a golden orb-weaver spider

Male preference for high-quality females is expected to evolve when male reproductive potential is restricted. However, when there is competition among males, some models predict the evolution of assortative male mate choice, in which good competitors choose high-quality females while poor competitors choose lower quality females to avoid competition. In Trichonephila clavipes spiders, males have limited sperm supply and fight for access to females. We tested whether female quality and male size (a proxy of fighting ability) influence male decisions in T. clavipes. We used field experiments in which males could choose between two available females in a scenario free of competition. We found that males choose their mates based on both female size and female recent pairing status (whether the female was accompanied by a male before the experiment). Importantly, male mate choice was plastic, and varied with male size, as large males preferred larger females that were recently unpaired, medium-sized males showed no preference and small males preferred smaller, recently paired females. Because all females appear to attract males, we predict that variation in male mate choice attenuates sexual selection on females. Our findings confirm the prediction of variable male mate choice when there is male–male competition and male reproductive potential is restricted, a pattern that may be common, but hard to detect.

Description of Two New Species of Philometra Costa, 1845 (Nematoda: Philometridae) from Marine Fishes off Japan, with Notes on Philometroides seriolae (Yamaguti, 1935).

Philometrid nematodes (Philometridae) represent a group of more than 200 species parasitic in the body cavity and various body tissues of fishes. Due to morphological and biological peculiarities, the majority of them are known only by their large females. Generally, the fauna of these parasites remains little known. Occasional helminthological examinations of three species of marine fishes in Japan revealed two new and one insufficiently known species of these tissue-dwelling parasites. These were studied with the use of light and scanning electron microscopy. All three nematode species are described. Philometra ostorhinchi sp. nov. (males and females) from the ovary of Ostorhinchus semilineatus (Temminck et Schlegel) (Apogonidae, Perciformes) is characterized mainly by the lengths and structure of spicules and the gubernaculum (spicules 108-120µm long, length of the gubernaculum 78-87µm); it is the only species of philometrids parasitic in a fish belonging to the Apogonidae. The gravid females of Philometra tenuis sp. nov. (only females available) from the head subcutaneous tissues of Conger myriaster (Brevoort) (Congridae, Anguilliformes) differ from congeners mainly in an unusual shape of the anterior oesophageal bulb. Some new data on the morphology of an insufficiently known species Philometroides seriolae (Ishii, 1931), collected from the body musculature of Seriola quinqueradiata Temminck et Schlegel (Carangidae, Perciformes), are provided; the number and arrangement of cephalic papillae in subgravid females of P. seriolae were found to be similar to those in females of the majority of other philometrid species. The present study extends the knowledge of the species composition of philometrids parasitizing marine fishes and of the morphology of P. seriolae, the type species of Philometroides Yamaguti, 1935.

Demographic factors affecting population growth in giant gartersnakes

ABSTRACTDemographic models provide insight into which vital rates and life stages contribute most to population growth. Integral projection models (IPMs) offer flexibility in matching model structure to a species’ demography. For many rare species, data are lacking for key vital rates, and uncertainty might dissuade researchers from attempting to build a demographic model. We present work that highlights how the implications of uncertainties and unknowns can be explored by building and analyzing alternative models. We constructed IPMs for the threatened giant gartersnake (Thamnophis gigas) based on published studies to determine where management efforts could be targeted to have the greatest effect on population persistence and what unknowns remain for future research. Given uncertainty in the survival of snakes during their first year, and in the form of the size‐survival relationship, we modeled a range of scenarios and evaluated where models agree about factors influencing population growth and where discrepancies exist. For most scenarios, the survival of large adult females had the greatest influence on population growth, but the relative importance of juvenile versus adult somatic growth for population growth was dependent on the recruitment probability and the shape of the size‐survival function. More data on temporal variation and covariance among vital rates would improve stochastic models for the giant gartersnake. This paper demonstrates the effectiveness of IPMs for studying the demography of reptiles and the value of the model‐building process for formalizing what is known and unknown about the demography of rare species. Published 2019. This article is a U.S. Government work and is in the public domain in the USA.

The role of functional constraints in nonrandom mating patterns for a dance fly with female ornaments.

Most hypotheses to explain nonrandom mating patterns invoke mate choice, particularly in species that display elaborate ornaments. However, conflicting selection pressures on traits can result in functional constraints that can also cause nonrandom mating patterns. We tested for functional load-lifting constraints during aerial copulation in Rhamphomyia longicauda, a species of dance fly that displays multiple extravagant female-specific ornaments that are unusual among sexual traits because they are under stabilizing selection. R.longicauda males provide females with a nuptial gift before engaging in aerial mating, and the male bears the entire weight of the female and nuptial gift for the duration of copulation. In theory, a male's ability to carry females and nuptial gifts could constrain pairing opportunities for the heaviest females, as reported for nonornamented dance flies. In concert with directional preferences for large females with mature eggs, such a load-lifting constraint could produce the stabilizing selection on female size previously observed in this species. We therefore tested whether wild-caught male R.longicauda collected during copulation were experiencing load-lift limitations by comparing the mass carried by males during copulation with the male's wing loading traits. We also performed permutation tests to determine whether the loads carried by males during copulation were lighter than expected. We found that heavier males are more often found mating with heavier females suggesting that whereas R.longicauda males do not experience a load-lift constraint, there is a strong relationship of assortative mating by mass. We suggest that active male mate choice for intermediately adorned females is more likely to be causing the nonrandom mating patterns observed in R.longicauda.

A new baenid turtle, Saxochelys gilberti, gen. et sp. nov., from the uppermost cretaceous (Maastrichtian) Hell Creek Formation: sexual dimorphism and spatial niche partitioning within the most speciose group of Late Cretaceous turtles

ABSTRACTThe uppermost Cretaceous (Maastrichtian) Hell Creek Formation in North America has yielded a diverse assemblage of fossil turtles dominated by baenids. A population of over 30 individual skeletons from the Hell Creek Formation of North Dakota comprises a new baenid turtle, Saxochelys gilberti, increasing the number of recognized Hell Creek turtles to at least 26, 11 of which are baenids. Saxochelys gilberti is differentiated from all other baenids based on the presence of a nuchal scale, finely sculptured shell, absence of an omega-shaped femoral-anal sulcus, presence of an omega-shaped extragular-humeral sulcus, a cavum tympani that is relatively smaller than the diameter of the orbit, presence of a robust single scale on the posteromedial portion of the parietals, and jugal exclusion from the orbital margin. Two distinct plastral morphologies, concave (N = 8) and flat (N = 9), are interpreted as representing male and female individuals, respectively. A ca. 10% size difference between the sexes indicates that S. gilberti is a sexually size-dimorphic turtle with larger females. This suggests female mate choice in this baenid turtle. A referred S. gilberti skeleton from above the Cretaceous–Paleogene boundary provides evidence for the survival of yet another species of turtle across this extinction event. The type locality of S. gilberti is close both stratigraphically and geographically to another locality consisting of a completely different assortment of baenid species, suggesting a fine degree of spatial niche partitioning in baenid turtles that may help explain the extremely high diversity of the group within the Hell Creek Formation.

Larger body size and earlier run timing increase alewife reproductive success in a whole lake experiment

Environmental conditions can influence biological characteristics, such as phenology and body size, with important consequences for organismal fitness. Examining these fitness consequences under natural conditions through genetic pedigree reconstruction offers a lens into potential population responses to changing environments. Over 3 years (2013–2015), we introduced adult alewife (Alosa pseudoharengus), anadromous, iteroparous clupeids, into one Massachusetts (USA) lake to complete the first detailed examination of this species’ mating system and assess relationships among body size, reproductive timing, and seasonal reproductive success. We reconstructed pedigrees using 15 microsatellites and genotypes from all possible parents and samples of naturally produced offspring within 4 months of hatching. In each of the 3 study years, spawning adults had multiple mates and spawned multiple times. Larger females that arrived and were translocated earlier had higher reproductive success. Declining body size and altered migration timing, through an influence on reproductive success, can influence population vital rates and productivity over time.

Biología reproductiva de &lt;i&gt;Boana pulchella&lt;/i&gt; y &lt;i&gt;Boana punctata&lt;/i&gt; (Anura: Hylidae) en poblaciones simpátricas de humedales templados

Boana pulchella habita principalmente climas templados y B. punctata principalmente climas tropicales, lo que permitiría suponer la presencia de estrategias reproductivas diferentes, aún en la región en la que sus poblaciones son simpátricas. En el presente estudio se analizaron y compararon los ciclos reproductivos, parámetros reproductivos y desarrollo de cuerpos grasos (CG) de Boana pulchella y B. punctata en humedales templados del río Paraná Medio. Boana pulchella presentó óvulos maduros de marzo a diciembre. En machos no hubo variación del volumen testicular a lo largo del año y el mayor desarrollo de CG de los machos se observó en invierno. Esta especie presentó un patrón reproductivo continuo. La vitelogénesis de B. punctata se inició en enero, alcanzando el mayor desarrollo ovárico en febrero (verano) y decreciendo hacia mayo (otoño). Los machos presentaron crecimiento testicular en verano, decreciendo hacia otoño y los CG presentaron su máximo desarrollo en enero para ambos sexos. Esta especie mostró un patrón reproductivo continuo. Ambas especies presentaron dimorfismo sexual con hembras que poseen una relación proporcional entre la talla y la inversión reproductiva. Boana pulchella presentó un mayor esfuerzo reproductivo (ER = 20,48 ± 12,9) y factor de tamaño ovárico (FTO = 25,73) que B. punctata (ER = 10,06 ± 4,45; FTO = 8,99). También se encontraron diferencias interespecíficas en la masa ovárica, complemento ovárico y volúmen testicular, siendo estas variables proporcionalmente mayores en B. pulchella. Las diferencias observadas en las poblaciones simpátricas podrían relacionarse con el desarrollo de estrategias reproductivas bajo diferentes presiones evolutivas.Material suplementario: https://doi.org/10.15446/caldasia.v41n2.80604

Caudal region regeneration in a natural population of the morid fish Physiculus cyanostrophus in the tropical eastern Atlantic ocean.

The present study describes a remarkable caudal regeneration capacity of Physiculus cyanostrophus, a benthopelagic fish from the twilight zone. This trait reveals the ability of this particular morid to survive attacks that would be lethal in other species. In teleosts, the most widespread sublethal predation is confined to scale-eating and fin-nipping by specialized predators. In P. cyanosytrophus the larger sized individuals the greatest amount of tissue loss occurred in the caudal region (maximum 28 vertebrae, corresponding to 45% lost body length). The amount of regenerated tissue was independent of body losses and ranged between 5 and 19% of total length for the entire range of sizes. The frequency of regenerated individuals in the population increases with ontogeny (16.8–67.5%). Tissue losses represent a significant allocation of costs in terms of growth and offspring production. Nevertheless, regeneration capability decreases mortality in the large breeding females of a population, maximizing maternal fitness.

A first fecundity study of the female snow crab Chionoecetes opilio Fabricius, 1788 (Decapoda: Brachyura: Oregoniidae) of the newly established population in the Barents Sea

Abstract The snow crab Chionoecetes opilioFabricius, 1788 is a newly established species in the Barents Sea. Since the first individuals were recorded in 1996, the population has increased and a fishery was initiated in 2012. Mature female snow crab caught in the central Barents Sea were investigated with regards to fecundity. Ovigerous females (N = 185) ranged from 48 to 100 mm carapace width (CW). Fecundity was 15,000–184,000 eggs per female with 100% clutch fullness, and was positively related to body size (fecundity = 0.233 * CW2.944) consistent with relationships described for other snow crab populations. Eight females had less than 100% clutch fullness, two of which had only 10% clutch fullness along with an old shell, indicating senescence. Dry egg weight was on average 0.065 mg and was hardly affected by CW. Females across all sizes invest similarly in individual eggs, and potential size-dependent differences in fitness are more related to the number of eggs produced than to the investment into individual eggs. We conclude that the fecundity-at-size of females is overall comparable to that of other populations, although the presence of large females results in high maximum individual fecundity estimates.

Can pathogens optimize both transmission and dispersal by exploiting sexual dimorphism in their hosts?

Pathogens often rely on their host for dispersal. Yet, maximizing fitness via replication can cause damage to the host and an associated reduction in host movement, incurring a trade-off between transmission and dispersal. Here, we test the idea that pathogens might mitigate this trade-off between reproductive fitness and dispersal by taking advantage of sexual dimorphism in their host, tailoring responses separately to males and females. Using experimental populations of Daphnia magna and its bacterial pathogen Pasteuria ramosa as a test-case, we find evidence that this pathogen can use male hosts as a dispersal vector, and the larger females as high-quality resource patches for optimized production of transmission spores. As sexual dimorphism in dispersal and body size is widespread across the animal kingdom, this differential exploitation of the sexes by a pathogen might be an unappreciated phenomenon, possibly evolved in various systems.