Size-assortative nest preference in a paternal brooding blenny Rhabdoblennius ellipes (Jordan & Starks)

Field and laboratory studies were conducted to clarify the processes contributing to the size-assortative nest use by males of a paternal brooding blenny Rhabdoblennius ellipes . The use of natural and artificial nests by males in the field was highly size-assortative; males used smaller nests even when larger nests were available. Aquarium nest choice experiments without a competitive male strongly suggested that the size-assortative nest use by males is not the result of male–male competition for larger nests, but male preference for size-matched nests. Males were likely to choose nests on the basis of the nest entrance size rather than nest length and volume, suggesting that the size-assortative nest preference in this species is an adaptation to predation pressure against eggs and resident males.     

Size-assortative nest choice in the absence of competition in males of the sand goby,Pomatoschistus minutus

Synopsis Size-assortative choice of nest site is commonly found among fish with paternal care. This pattern can be explained either by the superior competitive ability of large males for preferred large nests, or by a choice of nest size that is related to the male's own body size. Choice of nest size was studied in males of a small marine fish, the sand goby Pomatoschistus minutus, by providing artificial nest sites in laboratory and field experiments. A positive correlation between nest size and male size, indicating a size-assortative nest choice process, was found in both aquarium and field experiments. This is argued to be the outcome of a preference for an optimal nest size and not to be due to competition, as (a) a surplus of nest sites was available to the individuals in nature; (b) in the aquarium experiments, single males of all sizes, when offered a choice between a smaller and a larger nest site, showed a preference for nests in proportion to their body size and not for the largest available nests; and (c) in the aquaria, when single males were offered only a small or only a large nest site, small males abstained from building nests in the large sites, whereas in the small nest sites males of all sizes built nests. My conclusion is that size assortative nest choice occurred in the absence of competition, which thus is not a necessary condition for size-assortative nesting, contrary to what is commonly assumed in many studies. This preference may represent a compromise (or trade-off) between the advantage of a nest large enough to accommodate many eggs and a smaller one with lower maintenance and defence costs.     

MODE OF SEXUAL SELECTION DETERMINED BY RESOURCE ABUNDANCE IN TWO SAND GOBY POPULATIONS

We used field observations and experiments to show that sexual selection in two populations of sand gobies, Pomatoschistus minutus (Pisces, Gobiidae), was affected by differences in resource availability. Male sand gobies rely on empty mussel shells for nest building and spawning. The two populations differed considerably in nest-site abundance and sexual-selection regimes. In one population nest sites were scarce, leading to stronger male-male competition over nests, a higher nest site colonization rate and reduced potential for female choice compared with the other population that had a surplus of nests. In the high-competition population, males were larger than females, perhaps as a response to selection, whereas the other population was not sexually size dimorphic. The results from the field were confirmed in a pool experiment that demonstrated the effect of nest abundance on nest occupancy and male reproductive success. Larger males were more successful in obtaining nest sites in both high and low nest availability treatments. Larger males were also favored by females as mating partners, but only in the treatment with surplus nest sites. Nest shortage was associated with an increased potential for intrasexual selection (measured as the coefficient of variation), whereas the potential for intersexual selection was increased when nests were common. In conclusion, nest-site abundance can influence the relative contribution of intrasexual competition and mate choice in a population. Hence, resource availability can contribute to within-species variation in mating patterns.     

Size-assortative nest choice by the Japanese fluvial sculpin in the presence of male-male competition

Nest choice by the Japanese fluvial sculpin Cottus pollux and its relationship to male reproductive success, was examined in a natural habitat, central Japan. The larger males tended to occupy the deeper nest cavities, suggesting size-assortative nest choice by the species. Stepwise regression analysis showed that cavity area was correlated positively to male reproductive success. Nest choice experiments without a competitive male indicated an absence of size-assortative nest choice, but larger males tended to choose a large nest when another male was present, suggesting that size-assortative nest choice by the species is attributable to male-male competition for large nests, such being related to a resource-defence polygynous mating system.     

Big is better: the importance of size for reproductive success in male Pomatoschistus minutus (Pallas) (Pisces, Gobiidae)

The sand goby, Pomatoschistus minutus , was used in aquarium experiments to study the importance of body size for the ability of males to gain access to nest sites and mates. When several male and female P. minutus were allowed to reproduce together, on average, half of the males built nests, and half of those males obtained eggs in their nests. Males with nests were significantly larger than males without nests, and nests with eggs belonged to males larger than the males with empty nests. In another experiment, when two males were competing for one nest, the largest male occupied the nest when both fish were put into the aquarium simultaneously. However, when the smaller male had been allowed to establish a nest before the larger male was introduced, the small male could usually retain the nest. Males with a body length < 50 mm did not build nests at all in the early part of the breeding season. In female choice experiments, no preference for larger males was found. Thus, male-male competition for nest sites and behavioural differences between different sized males seem to be the main factors influencing the non-random mating success in male P. minutus.     

Male and female preferences for nest characteristics under paternal care

Nests play a critical role for offspring development across the animal kingdom. Nest quality may contribute to the builder's extended phenotype and serve as an ornament during mate choice. We examined male and female nest choice in the common goby (Pomatoschistus microps), a benthic fish with male‐only parental care where females deposit eggs in male‐built nests. Using prebuilt nest models, we independently manipulated two candidate nest quality traits: (a) nest entrance width with a role in oxygen ventilation, and (b) extent of sand cover with a role in camouflage. In simultaneous choice trials, male gobies exhibited no preference for any nest model type. This suggests that initial characteristics of a nesting substrate have minor importance for males, which usually remodel the nest. Females were given a choice between two males occupying either entrance‐ or cover‐manipulated nests. The same pair of males was then exposed to a second female but now with alternated nest types assigned. Most females were consistent in choosing the same, typically the heavier male of the two regardless of nest properties. However, the females that chose the same nest regardless of the male preferred low over high sand coverage and narrow over wide nest entrance. Our results indicate that females base their mating decision on a combination of male phenotype and nest traits. While we found no indication that females are attracted to highly decorated nests, our study is the first in fishes to disentangle a preference for narrow (and thus more protective) nest entrances independent of nest coverage.     

Changes in sexual selection resulting from novel habitat use in the sand goby

Resource availability may determine local breeding systems and may also vary locally between different habitats, affecting the way individuals distribute themselves between these habitats. For nest-breeding fishes, nest site availability is a crucial resource that has been found to affect local sexual selection regimes and thus breeding systems. In this study, we compared the availability and size distribution of nest sites and their consequences for habitat preference, fish distributions and the breeding system in sand gobies ( Pomatoschistus minutus ) breeding in two different habitats. The usual breeding sites of sand gobies are shallow sandy beaches, but here we report their breeding in a novel environment, on rocky bottoms. We found obvious differences between the two habitats. The density of occupied nests was nearly 50 times higher in rock habitat than on sand bottoms. However, competition for nest sites was stronger on sand; nearly all natural nest sites found were in use and empty nest sites were occupied at a much higher rate on sand than in rock habitat. In addition to the numerical differences, nests were larger and contained more eggs in rock habitat than in sand habitat. Moreover, we found significant habitat-specific differences in fish size distribution. The intensity of intrasexual competition as a result of the degree of nest site availability explains the observed patterns within the habitats, but not between them. These habitat-related differences are better explained by the larger average size of nests on rocky bottoms. The effect of nest size on habitat preference was confirmed experimentally by laboratory experiments. When nest size did not differ between the habitats, gobies originating in the two environments showed an equal preference for the sand habitat.     

Role of histamine as a putative inhibitory transmitter in the honeybee antennal lobe

Background

Nests are built in various animal taxa including fish. In systems with exclusive male parental care, the choice of a nest site may be an important component of male fitness. The nest site may influence male attractiveness as a mate, and male, embryo, and juvenile survival probabilities. Reproductively active three-spined stickleback males establish and defend a territory in which they build a nest. Territories can differ remarkably in qualities that influence male and female reproductive success like predation risk or abiotic factors such as dissolved oxygen concentration or lighting conditions. The latter may be important because in sticklebacks the extended visual capability into the ultraviolet (UV) wave range plays a role in female mate choice. Males are thus expected to be choosy about the habitat in which they will build their nest.

Results

We tested nest-site choice in male three-spined sticklebacks with respect to different UV lighting conditions. Reproductively active males were given the simultaneous choice to build their nest either in an UV-rich (UV+) or an UV-lacking (UV-) environment. Males exhibited no significant nest-site preferences with respect to UV+ or UV-. However, larger males and also heavier ones completed their nests earlier.

Conclusion

We found that UV radiation as well as differences in luminance had no influence on nest-site choice in three-spined sticklebacks. Males that built in the UV-rich environment were not different in any trait (body traits and UV reflection traits) from males that built in the UV-poor environment. There was a significant effect of standard length and body mass on the time elapsed until nest completion in the UV experiment. The larger and heavier a male, the faster he completed his nest. In the brightness control experiment there was a significant effect only of body mass on the duration of nest completion. Whether nest building preferences with respect to UV lighting conditions are context dependent needs to be tested for instance by nest-site choice experiment under increased predation risk.     

Mate preference for multiple cues: interplay between male and nest size in the sand goby, Pomatoschistus minutus

Female mating preferences are often based on more than one cue.In empirical studies, however, different mate choice cues aretypically treated separately ignoring their possible interactions.In the current work, we studied how male body size and sizeof the male's nest jointly affect mate preferences of femalesand gobies, Pomatoschistus minutus. The females were givena binary choice between males that differed either in body sizeor size of their nest or both. We found that neither body sizenor size of the nest alone affected male attractiveness, buttogether these 2 cues had a significant effect. Specifically,large males were more popular among females when they had alarge nest than when they occupied a small nest. The resultssuggest that if interaction effects between multiple mate choicecues are not considered, there is a danger of ignoring or underestimatingthe importance of these cues in sexual selection by female choice.     

Have your cake and eat it too: male sand gobies show more parental care in the presence of female partners

Traditionally, male parental effort and mate attraction effortare expected to be in conflict as they compete for the sameresource budget. However, the quality of care provided by themale may be of a direct benefit to females and may provide animportant mate choice cue. In a laboratory experiment, we examinedhow males modified their parental behavior with respect to matingopportunity by allowing male sand gobies to mate with a singlefemale either in a big or small nest (a constraint on futuremating potential). We then exposed half of these males to thevisual stimulus from additional females and recorded male eggfanning and nest building (two components of care), courtshipbehavior, and reproductive success through out the brood cycle.We found that males fanned longer and more frequently and didmore nest construction in the presence of females and in bignests. Males guarding large nests courted females more thandid males guarding small nests. All males consumed eggs duringthe brood cycle, but complete clutch cannibalism was most frequentwhen males were guarding small nests in the absence of females.The pattern of filial cannibalism that we observed suggeststhat males prematurely terminated care when their reproductivepotential was low, that is, when there was little nest spacefor additional mating and no mates present. We found no supportfor a trade-off between mate attraction and parental care. Indeed,taken together our results suggest that males may use parentalcare as a courtship strategy and that males who invest in mateattraction also have higher parental effort.     

Spatial and temporal patterns of nest distribution influence sexual selection in a marine fish

In many species, the natural distribution of material resources important for reproduction can profoundly impact reproductive success among individuals and, hence, the opportunity and intensity of sexual selection. Here, we report on a field‐based experiment investigating the effects of nest aggregation on sexual selection in a fish, the sand goby Pomatoschistus minutus. We found that the distribution of potential nests (sparse versus aggregated nest treatments) affected patterns of nest colonization and reproductive success. Specifically, in the treatment with aggregated nesting resources, a greater proportion of nests remained unoccupied by sand goby males. Although the size of nesting males did not differ between treatments, eggs accumulated more rapidly when nests were sparsely distributed. We found that the opportunity for selection decreased over time with the accumulation of eggs in the nests in both the aggregated and sparse treatments. Moreover, the effect of male size on reproductive success was influenced by an interaction between nest distribution and time, with the selection gradient being highest right after nest colonization when nests were aggregated, while the opposite pattern was observed in the sparse nest treatment. Such findings highlight the vital role that environmental and social factors can play in determining the importance of male phenotypic traits (in this case, male size). More broadly, our results also underscore how the natural distribution of resources, both in space and time, can impact the strength of sexual selection acting on wild animal populations.     

Effects of resource holding potential and resource value on tenure at nest sites in sand gobies

Over a broad range of animal systems, male reproductive successdepends on resource holding potential (RHP) and resource quality.In a field study, we randomly combined males of different sizeswith nests of different sizes to investigate the relative roleof resource holding potential and resource quality in determininga sand goby, Pomatoschistus minutus, male's nest tenure. Individuallymarked small and large males were given either small or largeflowerpots for nests in isolation and were exposed to intrudersafter they had built nests. We found that nest tenure was longerfor big males and owners of big nests. In most cases (34 of51) the original nest owner was replaced by a bigger male. Thesereplacements by larger males were probably due to takeoversby stronger intruders. Replacement males were larger at bignests. Our results support resource defense theory, as individualswith higher RHP and more valuable resources defended their nestfor longer. On nine occasions males abandoned their nests. Ownersof these nests were larger than the nest owners that were replaced.Hence, our results may provide an example of a situation inwhich sand goby males are able to judge the reproductive valueof their current situation and act accordingly.     

Seasonal variation in male alternative reproductive tactics

Genetic parentage analyses reveal considerable diversity in alternative reproductive behaviours (e.g. sneaking) in many taxa. However, little is known about whether these behaviours vary seasonally and between populations. Here, we investigate seasonal variation in male reproductive behaviours in a population of two‐spotted gobies (Gobiusculus flavescens) in Norway. Male two‐spotted gobies guard nests, attract females and care for fertilized eggs. We collected clutches and nest‐guarding males early and late in the breeding season in artificial nests and used microsatellite markers to reconstruct parentage from a subset of offspring from each nest. We hypothesized that mating, reproductive success and sneaking should be more prevalent early in the breeding season when competition for mates among males is predicted to be higher. However, parentage analyses revealed similar values of mating, reproductive success and high frequencies of successful sneaking early (30% of nests) and late (27% of nests) in the season. We also found that multiple females with eggs in the same nest were fertilized by one or more sneaker males, indicating that some males in this population engage in a satellite strategy. We contrast our results to previous work that demonstrates low levels of cuckoldry in a population in Sweden. Our results demonstrate marked stability in both the genetic mating system and male alternative reproductive tactics over the breeding season. However, sneaking rates may vary geographically within a species, likely due to local selection influencing ecological factors encountered at different locations.     

Unexpected male choosiness for mates in a spider

Sexual selection theory traditionally considers choosiness for mates to be negatively related to intra-sexual competition. Males were classically considered to be the competing, but not the choosy, sex. However, evidence of male choosiness is now accumulating. Male choosiness is expected to increase with an individual's competitive ability, and to decrease as intra-sexual competition increases. However, such predictions have never been tested in field conditions. Here, we explore male mate choice in a spider by studying size-assortative pairing in two natural sites that strongly differ in the level of male-male competition. Unexpectedly, our results demonstrate that mate choice shifts from opportunism to high selectivity as competition between males increases. Males experiencing weak competition did not exhibit size-related mating preferences. By contrast, when competition was intense we found strong size-assortative pairing due to male choice: while larger, more competitive males preferentially paired with larger, more fecund females, smaller males chose smaller females. Thus, we show that mating preferences of males vary with their competitive ability. The distinct preferences exhibited by males of different sizes seem to be an adaptive response to the lower reproductive opportunities arising from increased competition between males.     

Breeding pattern and nest guarding in Sicyopterus lagocephalus, a widespread amphidromous Gobiidae

Amphidromous gobies are usually nest spawners. Females lay a large number of small eggs under stones or onto plant stems, leaves or roots while males take care of the clutch until hatching. This study investigates the breeding pattern and paternal investment of Sicyopterus lagocephalus in a stream on Reunion Island. In February 2007 and January 2010, a total of 170 nests were found and the presence of a goby was recorded at 61 of them. The number of eggs in the nests ranged from 5,424 to 112,000 with an average number of 28,629. We showed that males accepted a single female spawning in the nest and cared for the eggs until hatching. The probability for a nest to be guarded increased with the number of eggs within it, suggesting that paternal investment depends on a trade-off between the reproductive value of the current reproduction and future nesting events. We showed that large nest stones were occupied by large males (TL >80 mm), whereas smaller males (TL <50 mm) were found under smaller cobbles, probably because of male–male competition for available nests. Our results suggest that the male’s choice relies upon a similarity to the female size, while the female’s choice was based on both body and nest stone sizes.     

Independent Mating Preferences for Male Body Size and Coloration in Female Trinidadian Guppies

Although females in numerous species generally prefer males with larger, brighter and more elaborate sexual traits, there is nonetheless considerable intra‐ and interpopulation variation in mating preferences amongst females that requires explanation. Such variation exists in the Trinidadian guppy, Poecilia reticulata, an important model organism for the study of sexual selection and mate choice. While female guppies tend to prefer more ornamented males as mates, particularly those with greater amounts of orange coloration, there remains variation both in male traits and female mating preferences within and between populations. Male body size is another trait that is sexually selected through female mate choice in some species, but has not been examined as extensively as body coloration in the guppy despite known intra‐ and interpopulation variation in this trait among adult males and its importance for survivorship in this species. In this study, we used a dichotomous‐choice test to quantify the mating preferences of female guppies, originating from a low‐predation population in Trinidad, for two male traits, body length and area of the body covered with orange and black pigmentation, independently of each other. We expected strong female mating preferences for both male body length and coloration in this population, given relaxation from predation and presumably relatively low cost of choice. Females indeed exhibited a strong preference for larger males as expected, but surprisingly a weaker (but nonetheless significant) preference for orange and black coloration. Interestingly, larger females demonstrated stronger preferences for larger males than did smaller females, which could potentially lead to size‐assortative mating in nature.     

Social status-dependent nest choice of territorial males under reproductive parasitism in a Lake Tanganyika cichlid Telmatochromis vittatus

Field and laboratory studies were conducted to examine how territorial males of a Lake Tanganyika cichlid Telmatochromis vittatus balance the conflicting demands on nest choice between occupying large nests with more females and avoiding reproductive parasitism (nest piracy, which is adopted by the largest males in the population). Pirates less frequently intruded the nests farther from neighbours, perhaps due to the costs associated with travelling between nests. The field experiment showed that territorial male T. vittatus sacrificed the fitness benefits that large nests offer and instead prioritized occupying the nests farther from neighbours on which fewer pirates intruded. The field observations suggested that they adopt different strategies for nest choice according to their relative competitive ability to pirates; the large territorial males, who are size-matched to pirates and can defend their nests against them, compete for larger nests among the more-isolated nests, whereas subordinate territorial males, which are smaller than pirates and thus inferior to them, compete for the more-isolated nests among the less-isolated nests. These findings suggest that the territorial male T. vittatus chooses the more-isolated nests to avoid pirate males at the expense of occupying large nests.     

Threat-sensitive Nest Preferences in Male Upland Bullies,Gobiomorphus breviceps

A male's ability to acquire and defend a nest site against competitors is an important requirement for successful breeding in many fish species. In the upland bully Gobiomorphus breviceps (Eleotridae), not all males are successful in gaining ownership of nesting rocks; therefore, male-male competition may be important in nest acquisition. Although larger nests have the potential to hold more eggs, in nature there is a preferred nest size well below the maximum available. I found that in over 88% of dyadic contests, the larger male was successful in acquiring the single nesting site provided. When males were individually given a choice of two artificial nest rocks, they consistently preferred the larger nest. These results suggest that larger males have the ability to occupy the largest nests. In the presence of a trout predator, males preferred nests with three closed sides 93% of the time. This preference disappeared when the threat was a conspecific. This shows that while males were choosing the larger nests their decisions were also threat-sensitive.     

The different roles of the roof density and nest size in the Iberian magpie nest

Nest volume in magpies is modulated by sexual selection. However, density of material that compounds the nest could also affect sexual signalling, and we may expect that high-quality pairs build larger and denser nests, with these two variables being positively correlated. As found for nest volume, density of nest thatching should be negatively related with laying date, which is indicative of pair quality. Alternatively, these traits could be subjected to different selective pressures and, hence, indicate different qualities. Results of the present study on a population of magpies in the Iberian Peninsula showed no relationship between nest volume and roof density. However, roof density was positively correlated to laying date, so that those nests that are built at later dates tend to have denser roof material. These data support the theory that density of roof material is related to nest predation, as there is a greater risk of predation at the end of the breeding season. Thus, nest volume and roof density could be two independent elements of a magpie’s nest, which have different ecological roles, as they would be subjected to different selection pressures. I suggest that nest size is a predictor of parental quality as has been previously demonstrated, while roof structure (roof density) is related to predation risk.     

Experimental Evidence that Sexual Displays are Costly for Nest Survival

Nest predation is one of the most significant limitations for successful breeding of tropical passerines. Thus, parental strategies may include choosing appropriate nest sites and behaving in ways that minimize predation. Habitat characteristics that may influence nest success include degree of nest concealment, proximity to habitat edge, plant architecture as well as several others cited in the literature. However, few studies have examined display behavior as a factor that could also influence nest survival. We experimentally tested whether sexual motor displays served as a cue for visually oriented predators to locate artificial nests in a population of blue‐black grassquits Volatinia jacarina, a Neotropical passerine that exhibits a complex sexual display and is subjected to elevated rates of nest predation. We also evaluated the effect of nest substrate on survival. Predation rate was higher for nests within territories of displaying males relative to areas without displaying males and for nests placed in shrubs relative to grasses. Predation increased sharply in the third experimental replicate, at the end of the breeding season, which suggests that predators may develop a search image for nests or may become more abundant during specific periods of the season. Avian predators appear to be the most important nest predators. Results suggest that there may be a trade‐off between the increase in fitness derived from sexual displays of males to attract potential mates and the decrease owing to predation of active nests within their territories.