The Direct Reproductive Cost of Same-Sex Attraction: Evidence from Two Nationally Representative U.S. Samples.

Same-sex attraction is associated with a direct reproductive cost, i.e., a reduced number of biological children. The current study aimed to assess this cost for different forms of sexual attraction (i.e., only attracted to opposite sex, mostly attracted to opposite sex, equally attracted to both sexes, mostly attracted to same-sex, only attracted to same-sex), using two large nationally representative datasets (N = 15,208) from the USA. The results indicated that same-sex attraction was associated with substantial loss in direct reproductive output. More specifically, significant differences between the different types of same-sex attraction were found: Exclusive and mostly homosexual orientation identities were associated with the highest direct reproductive cost, while mostly attracted to opposite sex orientation and bisexuality identities were associated with lower direct reproductive costs. In addition, bisexual women did not differ significantly from exclusively heterosexual women in terms of their reproductive output. The implications of these findings for the evolutionary origins of same-sex attraction are further discussed.

What drives the shift between sexual and clonal reproduction of Caragana stenophylla along a climatic aridity gradient?

BACKGROUND: The reasons that clonal plants shift between sexual and clonal reproduction have persisted as a knowledge gap in ecological literature. We hypothesized that clonal plants' shifts between sexual and clonal reproduction in different environments are driven by the relative costs of sexual and clonal reproduction. Moreover, we hypothesized plants prioritize sexual reproduction over clonal reproduction. To test these hypotheses, we determined the costs of sexual and clonal reproduction, and proportions of sexual and clonal reproduction of Caragana stenophylla along a climatic aridity gradient (semi-arid, arid, very arid and intensively arid zones) in the Inner Mongolia Steppe using several complementary field experiments. RESULTS: The cost of sexual reproduction increased while the cost of clonal reproduction decreased as climatic drought stress increased from the semi-arid to the intensively arid zones. The changes in the costs of these reproductive modes drove a shift in the reproductive mode of C. stenophylla from more sexual reproduction in the semi-arid zone to more clonal propagation in the intensively arid zone. However, because of the evolutionary advantages of sexual reproduction, sexual reproduction still held priority over clonal production in C. stenophylla, with the priority of sexual reproduction gradually increasing from the semi-arid to the intensively arid zones. CONCLUSIONS: Our study suggested that sexual reproduction has relatively high priority in propagation of C. stenophylla. However, if the costs of sexual reproduction are too high, C. stenophylla likely chooses clonal reproduction, and the ratio between sexual and clonal reproduction could be mediated by reproductive cost. These reproductive strategies reflect optimal resource utilization, and allow the persistence of both reproductive modes across stressful conditions depending on their evolutionary advantages.

Testing the heat dissipation limit theory in a breeding passerine.

The maximum work rate of animals has recently been suggested to be determined by the rate at which excess metabolic heat generated during work can be dissipated (heat dissipation limitation (HDL) theory). As a first step towards testing this theory in wild animals, we experimentally manipulated brood size in breeding marsh tits (Poecile palustris) to change their work rate. Parents feeding nestlings generally operated at above-normal body temperatures. Body temperature in both males and females increased with maximum ambient temperature and with manipulated work rate, sometimes even exceeding 45°C, which is close to suggested lethal levels for birds. Such high body temperatures have previously only been described for birds living in hot and arid regions. Thus, reproductive effort in marsh tits may potentially be limited by the rate of heat dissipation. Females had lower body temperatures, a possible consequence of their brood patch serving as a thermal window facilitating heat dissipation. Because increasing body temperatures are connected to somatic costs, we suggest that the HDL theory may constitute a possible mediator of the trade-off between current and future reproduction. It follows that globally increasing, more stochastic, ambient temperatures may restrict the capacity for sustained work of animals in the future.

Female in-nest chatter song increases predation.

Female song is an ancestral trait in songbirds, yet extant females generally sing less than males. Here, we examine sex differences in the predation cost of singing behaviour. The superb fairy-wren (Malurus cyaneus) is a Southern Hemisphere songbird; males and females provision the brood and produce solo song year-round. Both sexes had higher song rate during the fertile period and lower song rate during incubation and chick feeding. Females were more likely than males to sing close to or inside the nest. For this reason, female but not male song rate predicted egg and nestling predation. This study identifies a high fitness cost of song when a parent bird attends offspring inside a nest and explains gender differences in singing when there are gender differences in parental care.

Changing motivations during migration: linking movement speed to reproductive status in a migratory large mammal.

A challenge in animal ecology is to link animal movement to demography. In general, reproducing and non-reproducing animals may show different movement patterns. Dramatic changes in reproductive status, such as the loss of an offspring during the course of migration, might also affect movement. Studies linking movement speed to reproductive status require individual monitoring of life-history events and hence are rare. Here, we link movement data from 98 GPS-collared female moose (Alces alces) to field observations of reproductive status and calf survival. We show that reproductive females move more quickly during migration than non-reproductive females. Further, the loss of a calf over the course of migration triggered a decrease in speed of the female. This is in contrast to what might be expected for females no longer constrained by an accompanying offspring. The observed patterns demonstrate that females of different reproductive status may have distinct movement patterns, and that the underlying motivation to move may be altered by a change in reproductive status during migration.

Effects of past mating behavior versus past ejaculation on male mate choice and male attractiveness.

Past reproductive effort allows males to assess their ability to acquire mates, but it also consumes resources that can reduce their future competitive ability. Few studies have examined how a male's reproductive history affects his subsequent mate choice, and, to date, no study has determined the relative contribution of past mating behavior and past ejaculate production because these two forms of investment are naturally highly correlated. Here, we disentangled the relative effects of past mating behavior and past ejaculate production in mosquitofish (Gambusia holbrooki) by experimentally preventing some males from ejaculating when trying to mate. We assessed the effect of mating behavior on mate choice by comparing males that had previously been with or without access to females and male rivals for 8 and 16 weeks and assessed the effect of ejaculation on mate choice by comparing males that either could or could not ejaculate when they had access to females for 16 weeks. Reproductive treatment did not affect male attractiveness, but it did affect male mate choice. Somewhat surprisingly, in five of the six treatment-by-age at testing combinations, males preferred a female in the vicinity of a male rival over a solitary female. This preference was marginally stronger for males that had previously engaged in mating behavior but were unaffected by past ejaculate production. We discuss the potential benefits to males of associating with another male when seeking mates. This is the first study to quantify the relative influence of pre- and post-copulatory reproductive investment on male mate choice.

Hatching date influences winter habitat occupancy: Examining seasonal interactions across the full annual cycle in a migratory songbird.

Birds experience a sequence of critical events during their life cycle, and past events can subsequently determine future performance via carry-over effects. Events during the non-breeding season may influence breeding season phenology or productivity. Less is understood about how events during the breeding season affect individuals subsequently in their life cycle. Using stable carbon isotopes, we examined carry-over effects throughout the annual cycle of prairie warblers (Setophaga discolor), a declining Nearctic-Neotropical migratory passerine bird. In drier winters, juvenile males that hatched earlier at our study site in Massachusetts, USA, occupied wetter, better-quality winter habitat in the Caribbean, as indicated by depleted carbon isotope signatures. For juveniles that were sampled again as adults, repeatability in isotope signatures indicated similar winter habitat occupancy across years. Thus, hatching date of juvenile males appears to influence lifetime winter habitat occupancy. For adult males, reproductive success did not carry over to influence winter habitat occupancy. We did not find temporally consecutive "domino" effects across the annual cycle (breeding to wintering to breeding) or interseasonal, intergenerational effects. Our finding that a male's hatching date can have a lasting effect on winter habitat occupancy represents an important contribution to our understanding of seasonal interactions in migratory birds.

Effect of nutritional state and dispersal on the reproductive efficiency in Triatoma infestans (Klug, 1834) (Hemiptera: Reduviidae: Triatominae) susceptible and resistant to deltamethrin.

The dispersal of insects is determinant in the colonization of new areas and the propagation of insecticide resistance. Nutritional status and reproductive characteristics determine the colonization capacity after the dispersal event. Studies about of the effects of dispersal on reproduction in triatomines are few and none in resistant insects. The aim was to determine the effects of nutritional state and dispersal on the subsequent reproductive potential in Triatoma infestans (Klug, 1834) susceptible and resistant to deltamethrin. Three nutritional states were obtained with the number of feeds (NF) offered (0, 1 or 2). The resistant females were evaluated only with NF1. The experimental arena was 10 m long and contained two shelters. Groups of 30 virgin females of each NF were released in one of the shelters and were able to move during 3 days/nights. Females without possibility of dispersal were the controls. The reproductive parameters were determined on the couples between the experimental females and males from the breeding. The results showed that most of the females dispersed by walking. The dispersal had effects on the reproduction of the deltamethrin-susceptible females and this depended on the number of feeds. Fecundity, fertility and the proportion of females that oviposited were higher in females dispersed with two feeds but was lower in females dispersed with less feeds. In addition, the effect of the dispersal on the reproduction and the life time also depended of the toxicological phenotype. The resistant insect oviposited in higher proportion and showed greater fecundity and more weeks of life when they dispersed that when they did not do it, and was opposite to that observed in susceptible ones. Finally, the resistance to insecticide had an effect on the reproduction and the life span and this effect depended on whether the insects dispersed or not.

Effect of breeding performance on the distribution and activity budgets of a predominantly resident population of black-browed albatrosses.

Pelagic seabirds breeding at high latitudes generally split their annual cycle between reproduction, migration, and wintering. During the breeding season, they are constrained in their foraging range due to reproduction while during winter months, and they often undertake long-distance migrations. Black-browed albatrosses (Thalassarche melanophris) nesting in the Falkland archipelago remain within 700 km from their breeding colonies all year-round and can therefore be considered as resident. Accordingly, at-sea activity patterns are expected to be adjusted to the absence of migration. Likewise, breeding performance is expected to affect foraging, flying, and floating activities, as failed individuals are relieved from reproduction earlier than successful ones. Using geolocators coupled with a saltwater immersion sensor, we detailed the spatial distribution and temporal dynamics of at-sea activity budgets of successful and failed breeding black-browed albatrosses nesting in New Island, Falklands archipelago, over the breeding and subsequent nonbreeding season. The 90% monthly kernel distribution of failed and successful breeders suggested no spatial segregation. Both groups followed the same dynamics of foraging effort both during daylight and darkness all year, except during chick-rearing, when successful breeders foraged more intensively. Failed and successful breeders started decreasing flying activities during daylight at the same time, 2-3 weeks after hatching period, but failed breeders reached their maximum floating activity during late chick-rearing, 2 months before successful breeders. Moon cycle had a significant effect on activity budgets during darkness, with individuals generally more active during full moon. Our results highlight that successful breeders buffer potential reproductive costs during the nonbreeding season, and this provides a better understanding of how individuals adjust their spatial distribution and activity budgets according to their breeding performance in absence of migration.

Reproduction Immunity Trade-Off in a Mollusk: Hemocyte Energy Metabolism Underlies Cellular and Molecular Immune Responses.

Immune responses, as well as reproduction, are energy-hungry processes, particularly in broadcast spawners such as scallops. Thus, we aimed to explore the potential reproduction-immunity trade-off in Argopecten purpuratus, a species with great economic importance for Chile and Peru. Hemocytes, key immunological cells in mollusks, were the center of this study, where we addressed for the first time the relation between reproductive stage, hemocyte metabolic energetics and their capacity to support immune responses at cellular and molecular levels. Hemocyte metabolic capacity was assessed by their respiration rates, mitochondrial membrane potential and citrate synthase (CS) activity. Cellular immune parameters such as the number of circulating and tissue-infiltrating hemocytes and their reactive oxygen species (ROS) production capacity were considered. Molecular immune responses were examined through the transcriptional levels of two pattern recognition receptors (ApCLec and ApTLR) and two anti-microbial effectors (ferritin and big defensin). Their expressions were measured in hemocytes from immature, matured and spawned scallops under basal, and one of the following challenges: (i) in vitro, where hemocytes were challenged with the ß glucan zymosan, to determine the immune potentiality under standardized conditions; or (ii) in vivo challenge, using hemocytes from scallops injected with the pathogenic bacteria Vibrio splendidus. Results indicate a post-spawning decrease in the structural components of the immune system (hemocyte number/quality) and their potential capacity of performing immune functions (with reduced ATP-producing machinery and exhaustion of energy reserves). Both in vitro and in vivo challenges demonstrate that hemocytes from immature scallops have, in most cases, the best metabolic potential (increased CS activity) and immune performances, with for example, over threefold higher ROS production and tissue-infiltration capacity than those from mature and spawned scallops after the bacterial challenge. Agreeing with cellular responses, hemocytes from immature individuals induced the highest levels of immune receptors and antimicrobial effectors after the bacterial challenge, while spawned scallops presented the lowest values. Overall, results suggest a trade-off between resource allocation in reproduction and the immune responses in A. purpuratus, with hemocyte energy metabolic capacity potentially underlying cellular and molecular immune responses. Further research would be necessary to explore regulatory mechanisms such as signaling pleiotropy which may potentially be underlying this trade-off.

Nest defence behavioural reaction norms: testing life-history and parental investment theory predictions.

Predation is the primary source of reproductive failure in many avian taxa and nest defence behaviour against predators is hence an important aspect of parental investment. Nest defence is a complex trait that might consistently differ among individuals (personality), while simultaneously vary within individuals (plasticity) according to the reproductive value of the offspring. Both complementary aspects of individual variation can influence fitness, but the causality of links with reproductive success remains poorly understood. We repeatedly tested free-living female great tits (Parus major) for nest defence (hissing) behaviour across the nesting cycle, by presenting them with a model predator. Hissing behaviour was highly repeatable but, despite population-level plasticity, we found no support for individual differences in plasticity. Path analysis revealed that repeatable differences in hissing behaviour had no direct effect on nest success or fledgling number. However, our best supported path-model showed that more fiercely hissing females laid smaller clutches, with clutch size in turn positively influencing fledgling number, suggesting that females are most likely facing a trade-off between investment in nest defence and reproduction. Strong stabilizing selection for optimal plasticity, in combination with life-history trade-offs, might explain the high repeatability of nest defence and its link with reproductive success.

The use of the nest for parental roosting and thermal consequences of the nest for nestlings and parents.

ABSTRACT: At temperate latitudes, altricial birds and their nestlings need to handle night temperatures well below thermoneutrality during the breeding season. Thus, energy costs of thermoregulation might constrain nestling growth, and low nocturnal temperatures might require resources that parents could otherwise have invested into nestlings during the day. To manipulate parental work rate, we performed brood size manipulations in breeding marsh tits (Poecile palustris). Nest box temperatures were always well above ambient temperature and increased with increasing brood size. In line with predictions, a large majority of females (but no males) made use of this benign environment for roosting. Furthermore, females tending enlarged broods, thereby having to work harder during the day, reduced their body temperature at night. This might have reduced nocturnal energy expenditure. Our finding that a higher proportion of enlarged, as compared to control, females continued to use the nest box as roosting sites even after a simulated predation event despite increased vulnerability to predation, further highlighting the need for energy conservation in this group. High nest box attendance and reduced body temperature in brood-reduced females may indicate that these females prioritised self-maintenance by initiating other costly physiological adjustments, e.g. moult, when relieved from parental work. We suggest that the energy demand for defending homeothermy is an element of the general trade-off between current and future reproduction, i.e. between daytime investment in food provisioning and the potential short- and long-term costs of a reduction in body temperature and increased predation risk. SIGNIFICANCE STATEMENT: Even during summer at temperate latitudes, breeding birds need to use energy to maintain stable body temperature. Parents, thus, need to enter the night with sufficient body reserves to cover energy requirements for thermoregulation. As these resources could be used for feeding nestling during the day, adaptations to reduce the cost of thermoregulation would be selected for. We performed brood size manipulations, thereby increasing the need for nestling provisioning in marsh tits (Parus palustris). We found that females typically spent the night in the thermally benign environment of the nest box together with their brood. Females working hard during the day continued to roost in the nest box during the night despite an increase in the perceived risk of nest predation. Furthermore, these females reduced their body temperature at night, thereby reducing the gradient between ambient and body temperature, further reducing the cost of thermoregulation.

Male-biased hermaphrodites in a gynodioecious shrub, Daphne jezoensis.

Gynodioecy, a state where female and hermaphrodite plants coexist in populations, has been widely proposed an intermediate stage in the evolutionary pathway from hermaphroditism to dioecy. In the gynodioecy-dioecy pathway, hermaphrodites may gain most of their fitness through male function once females invade populations. To test this prediction, comprehensive studies on sex ratio variation across populations and reproductive characteristics of hermaphrodite and female phenotypes are necessary. This study examined the variation in sex ratio, sex expression, flower and fruit production and sexual dimorphism of morphological traits in a gynodioecious shrub, Daphne jezoensis, over multiple populations and years. Population sex ratio (hermaphrodite:female) was close to 1:1 or slightly hermaphrodite-biased. Sex type of individual plants was largely fixed, but 15% of plants changed their sex during a 6-year census. Hermaphrodite plants produced larger flowers and invested 2.5 times more resources in flower production than female plants, but they exhibited remarkably low fruit set (proportion of flowers setting fruits). Female plants produced six times more fruits than hermaphrodite plants. Low fruiting ability of hermaphrodite plants was retained even when hand-pollination was performed. Fruit production of female plants was restricted by pollen limitation under natural conditions, irrespective of high potential fecundity, and this minimised the difference in resources allocated to reproduction between the sexes. Negative effects of previous flower and fruit production on current reproduction were not apparent in both sexes. This study suggests that gynodioecy in this species is functionally close to a dioecious mating system: smaller flower production with larger fruiting ability in female plants, and larger flower production with little fruiting ability in hermaphrodite plants.

Age-sex analysis for the diet of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in Shennongjia National Nature Reserve, China.

Age-sex differences in diet have been reported in many nonhuman primates, and body size, reproductive costs, and growth are three mutually non-exclusive factors often proposed to explain such differences. Smaller animals tend to feed on high quality foods (high in protein/energy) more often than larger animals due to their higher metabolic requirements per body weight. Animals of different sizes tend to use different substrate levels, leading to dietary differences if food resources are unevenly distributed along substrate levels. Adult females and juveniles experience additional metabolic requirements for reproduction and growth, respectively, and tend to feed on high quality foods more frequently than adult males. We conducted an age-sex analysis for the diet of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in Shennongjia, China. In spite of general age-sex similarities, we found that adult males ate herbs more frequently than juveniles and adult females, most likely because they were more terrestrial. As predicted, juveniles ate high quality foods (young leaves, fruits, seeds, and buds) more frequently, and meanwhile ate low quality foods (barks and lichens) less frequently than adult males across the study year or in some seasons when these food types were eaten. However, we found high similarities in diet between adult females and adult males. The most likely reason was that the low diversity of food sources and strong phenological synchrony did not allow adult females to select foods based on quality to cope with their higher metabolic constraints compared to adult males. Surprisingly, the only sex difference in diet except herbs was that adult females ate lichens more frequently in autumn. One plausible reason was that lactating females experienced their highest metabolic requirements in the middle period of infant care (autumn), and had to disproportionately increase the intake of lichens due to the limited availability of plant foods.

Brood reduction facilitates female but not offspring survival in the great tit.

The long-term fitness consequences of brood reduction were examined in two (urban and rural) great tit populations in south-eastern Estonia during 1987-1994. The brood reduction hypothesis in its initial, Lackian sense was not supported since partial brood loss was accompanied by a decrease in fledgling weight and recruitment rate. Female survival was significantly improved in broods with high nestling mortality in the rural population. My results suggest that female great tits might be able to reallocate resources for self-maintenance if food appears to be short for the successful raising of the brood. However, parents are not capable of efficiently reallocating resources between nestlings.

THE COST OF REPRODUCTION AND EXPERIENCE-DEPENDENT VITAL RATES IN A SMALL PETREL.

Life history theory predicts that higher levels of reproductive investment entail higher reproductive costs especially among young and inexperienced individuals that might not optimize reproductive investment. Using a long-term individual and state-dependent capture-recapture data on Storm Petrels (Hydrobates pelagicus) we analyzed whether breeding experience and current breeding investment were associated with the expression of the cost of reproduction in terms of reduced survival and/or future breeding performance. We found a positive relationship between current breeding investment, breeding experience, and future survival and an improvement in breeding performance with individual experience independently of the previous breeding outcome. Our results suggest that the survival cost paid by first-time breeders and the positive correlation between reproduction and survival corresponds to selection against low quality birds unrelated to the breeding effort. Our work outlines the need to investigate the effect of multiple individual traits on different life history trade-offs simultaneously.

THE EVOLUTION OF REPRODUCTIVE EFFORT IN SQUAMATE REPTILES: COSTS, TRADE-OFFS, AND ASSUMPTIONS RECONSIDERED.

We evaluated Shine and Schwarzkopf's (SS) model of the evolution of reproductive effort (RE) in squamate reptiles. They suggested that fecundity trade-offs were unimportant in the evolution of RE in most squamate reptiles and that only survival trade-offs needed to be considered. However, we show that by assuming no variation in offspring size exists, and that adult mortality is episodic, the results of the SS model are not general. By extension, we argue that conclusions drawn about factors important in the evolution of RE in squamate reptiles are premature. Using a modified version of the SS model, we demonstrate that variation in the form of trade-offs relating offspring size and survival substantially affect relationships among clutch size, relative clutch mass, and lifetime reproductive success. We also demonstrate that the way in which adult mortality is simulated drastically affects conclusions about the potential fecundity trade-offs experienced by populations of squamate reptiles. Finally, we suggest that a complete understanding of the evolution of RE will come from theory that incorporates trade-offs between offspring size and quality, as well as other system-specific constraints on the allocation of energy to growth, maintenance, storage, and reproduction.