Flexible Life History Strategies of Ninespine Sticklebacks,Genus <Emphasis Type="BoldItalic">Pungitius</Emphasis>

Synopsis We studied the life histories of the ninespine sticklebacks, Pungitius pungitius and Pungitius tymensis, collected from Japanese freshwater and brackish (sea) water habitats by examining the strontium (Sr) and calcium (Ca) concentrations in their otoliths. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat regardless of identification as freshwater or brackish water type based on morphological characteristics. The ninespine sticklebacks living in a freshwater environment showed consistently low Sr:Ca ratios throughout the otolith. These samples were identified as a standard freshwater type. In contrast, all freshwater-type fishes collected from the intertidal zone showed higher otolith Sr:Ca ratios than those in the standard freshwater type, and the ratios fluctuated with the growth phase. All brackish water-type fishes collected in the intertidal zone showed the highest otolith Sr:Ca ratio throughout the otolith. In the present study, besides the two representative life history types of P. pungitius, i.e., freshwater and brackish water life history types, other sticklebacks had an anadromous life history type. These findings clearly indicate that the ninespine stickleback has a flexible migration strategy with a high degree of behavioral plasticity and an ability to utilize the full range of salinity in its life history.     

Effect of salinity on nest building behaviour in the nine-spined stickleback Pungitius sinensis

The authors evaluated the adaptability of male nine-spined sticklebacks (Pungitius sinensis) at three salinity levels (0, 5 and 10 psu) by comparing nest building success rates with nest structures. Successful nest building decreased as salinity increased. In addition, nests built in fresh water (i.e., 0 psu) were glued together, whereas those built in brackish water (5 and 10 psu) broke easily and fell from the nest site to the gravel bottom. Based on these findings, the authors suggest that P. sinensis adapts to freshwater environments.     

Boldness and Stress Responsiveness as Drivers of Nest‐Site Selection in a Ground‐Nesting Bird

Nest‐site selection involves trade‐offs between the probability of nest discovery by egg predators, danger to the incubating parent from predators and provision of an appropriate microclimate for incubation, and all three components are potentially influenced by nest concealment and distance to habitat edge. Personality traits also affect habitat choice, and the trade‐off hypothesis suggests that variable stress‐coping strategies may evolve because individuals prioritize either productivity (proactive coping) or survival (reactive coping), both of which cannot be simultaneously maximized. Applying this hypothesis to understand nest‐site selection by female eider ducks (Somateria mollissima), we predicted that bold individuals with attenuated stress responsiveness should select concealed nests further away from the shore, thereby promoting clutch survival at the potential expense of reduced escape opportunities for themselves. In testing this prediction, we controlled for individual quality (female body condition and breeding experience) and verified that individual stress responses and nest‐site preferences were consistent by analysing their repeatability. Finally, we analysed how the viable proportion of the clutch was related to nest‐site and female characteristics. Our prediction was supported: bold females [short flight initiation distance (FID)] and those with lower handling‐induced body temperature were found in concealed nests, and bold females and those with lower handling‐induced corticosterone concentrations occupied nests farther from the shore. The viable proportion of the clutch peaked at intermediate proportional nest‐cover and increased linearly with increasing nest distance from the shore. Stress coping styles may thus be related to nest‐site selection, but their fitness consequences may be manifested indirectly through the nest‐site characteristics.     

Dyadic relationships in nesting males of the three-spined stickleback, Gasterosteus aculeatus

Multidimensional scaling analysis of nest site location, nesting interval, and aggressive and mating interactions revealed that male three-spined sticklebacks, Gasterosteus aculeatus, formed nesting clusters comprising five patterns of dyadic relationships. These patterns were defined by intervening variables such as size difference between the two males, nest site locations, synchronization of nesting cycles (egg presence in the nest), distance between two nests, and nest raiding behaviours. Several patterns of dyadic relationships were integrated among nesting males and their constellations indicated an expression of the social structure. Through an understanding the social structure, I described effects of social context or situations on individual reproductive success.     

Coastal saltpans are a good alternative breeding habitat for Kentish plover Charadrius alexandrinus when umbrella species are present

The loss and degradation of natural habitats in coastal areas worldwide has adversely affected many waterbird species, changing their breeding distribution and reducing their productivity. Anthropogenic habitats such as saltpans can provide alternative or complementary habitats for waterbirds and mitigate the increasing human impact on natural coastal habitats. Unvegetated linear paths between salt ponds are used by ground‐nesting waterbird species to breed but their linear structure may facilitate the detection of nests by predators. This negative effect may, however, be counterbalanced by the advantages of breeding in mixed colonies. To evaluate the importance and the risks of breeding in saltpans we used the Kentish plover Charadrius alexandrinus breeding in coastal saltpans of southern Portugal as a model species. Specifically, we assessed the role of nest‐site characteristics, predation and nesting proximity to species with aggressive antipredator behaviour (black‐winged stilt Himantopus himantopus) on their breeding success. Kentish plovers selected nest‐sites on the edges of paths, with about 20% of water around the nest, and a mean visibility of more than 72%; however nest‐site characteristics were not correlated with nesting success. Predation was the main cause of nest loss in saltpans (42%); carrion crows Corvus corone were responsible for most daylight nest predation (58%) and red fox (Vulpes vulpes; 73%) for night predation. An 8‐yr monitoring plan of a Kentish plover population showed a linear increase in their breeding success as their breeding season increasingly overlapped with that of the black‐winged stilt. An experiment with artificial nests showed a significant increase in the number of exposure days (7 to 12) when these nests were within close distance of black‐winged stilt nests. Overall, our results showed that saltpans are an important alternative breeding habitat for the Kentish plover, especially for the maintenance of mixed species colonies.     

Communal nesting under climate change: fitness consequences of higher incubation temperatures for a nocturnal lizard

Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures regulate nest temperatures. In southeastern Australia, velvet geckos Oedura lesueurii lay eggs communally inside rock crevices. We investigated whether increases in air temperatures could elevate nest temperatures, and if so, how this could influence hatching phenotypes, survival, and population dynamics. In natural nests, maximum daily air temperature influenced mean and maximum daily nest temperatures, implying that nest temperatures will increase under climate warming. To determine whether hotter nests influence hatchling phenotypes, we incubated eggs under two fluctuating temperature regimes to mimic current ‘cold’ nests (mean = 23.2 °C, range 10–33 °C) and future ‘hot’ nests (27.0 °C, 14–37 °C). ‘Hot’ incubation temperatures produced smaller hatchlings than did cold temperature incubation. We released individually marked hatchlings into the wild in 2014 and 2015, and monitored their survival over 10 months. In 2014 and 2015, hot‐incubated hatchlings had higher annual mortality (99%, 97%) than cold‐incubated (11%, 58%) or wild‐born hatchlings (78%, 22%). To determine future trajectories of velvet gecko populations under climate warming, we ran population viability analyses in Vortex and varied annual rates of hatchling mortality within the range 78– 96%. Hatchling mortality strongly influenced the probability of extinction and the mean time to extinction. When hatchling mortality was >86%, populations had a higher probability of extinction (PE: range 0.52– 1.0) with mean times to extinction of 18–44 years. Whether future changes in hatchling survival translate into reduced population viability will depend on the ability of females to modify their nest‐site choices. Over the period 1992–2015, females used the same communal nests annually, suggesting that there may be little plasticity in maternal nest‐site selection. The impacts of climate change may therefore be especially severe on communal nesting species, particularly if such species occupy thermally challenging environments.     

Brent Geese (<Emphasis Type="Italic">Branta bernicla</Emphasis>) Breeding Associations with Pomarine Skuas (<Emphasis Type="Italic">Stercorarius pomarinus</Emphasis>) on the Mainland Tundra

This article is based on data that were collected in the years 2000?2007, 2012, and 2014 in the vicinities of Medusa Bay (73°21′ N, 80°32′ E) and in 2002 at the mouth of the Uboynaya River (73°37′ N, 82°10′ E), in the northwestern part of the Taimyr Peninsula. In years when the abundance of lemmings is high, brent geese may breed not only near nests of snowy owls and rough-legged buzzards, but also sparsely in the mainland tundra, often without any protection. Some such nests are successfully incubated until hatching. A considerable part of these dispersed nests appears to be associated with a nest or territory of pomarine skuas that are able to scare away the main tundra predator, the arctic fox, to a distance of about 500 m from their nests. Brent geese that breed within this distance to theses nests gain additional protection against arctic foxes. However, brent geese do not display a tendency to place their nests closer to pomarine skua nests. The mean distance from geese nests to pomarine skua nests or centers of their territories comprised 2/3 of the mean distance between nests of pomarine skuas and turned out to be quite stable over the years and in two different tundra areas.     

Decision-making conditions for intra- or inter-nest mating of winged males in the male-dimorphic ant <Emphasis Type="Italic">Cardiocondyla minutior</Emphasis>

Only winged male and female ants generally mate through nuptial flight during the reproductive season. In the ants of Cardiocondyla, the males show wing dimorphism and their reproductive strategies differ depending on the differences in wing morphology. It has been suggested that wingless “ergatoid” males bearing very similar external morphologies to workers mate within natal nests, whereas winged males bearing typical ant male morphology disperse from their nests to mate. However, some behavioral observations suggest that the winged males of some Cardiocondyla ants such as C. obscurior and C. minutior may mate within natal nests before dispersion. We evaluated the factors affecting the mating behaviors of the winged males of C. minutior under laboratory conditions. We found that (1) the winged males remained and mated with virgin females in natal nests when either virgin winged females or the relatively mature pupae of winged females (i.e., at least 10 days) were present in the nest, (2) the winged males dispersed to adjacent nests with virgin winged females when only mated queens and the relatively young pupae of winged females (i.e., <9 days) were present in the nest, and (3) all winged males were accepted by the workers of non-natal nests irrespective of the distance from the natal nests in the field. Although most ergatoid males were accepted by the workers of close non-natal nests, they were all attacked and killed by the workers of distant non-natal nests. These results suggest that intra-nest mating and the dispersion of the winged males of C. minutior are facultatively determined by the condition of winged females (virginity and relative pupal age) in natal nests. Furthermore, our results suggest that winged males are likely to seek mating partners chemically and to mate with virgin winged females.     

Salinity and the distribution of Cladocera in Warri River,Nigeria

Hydrobiological investigations of the water quality and plankton of Warri River started in 1981, shortly before the commissioning of the Delta Steel Plant on the banks of the river at Aladja. The 150 km of river gradates from pure freshwater through brackish to marine and so provides a suitable habitat for a study of the limits of migration of any group of zooplankton. The Cladocera of Warri River consists of two bosminids, thirteen chydorids, three daphniids, three macrothricids, one moinid, and two sidids. All except the sididPenilia sp. are well known freshwater forms, which are limited in longitudinal distribution to areas with salinity below 2.5‰. Penilia sp. found in Warri River were restricted to the truely brackish-water areas with salinity values of 7‰ −8‰. In this respect they represent the first reported brackish water Cladocera in Africa. They also differ fromPenilia avirostris Dana found in marine habitats in certain morphological details, and so the Warri RiverPenilia may be a new taxon.     

Effects of down collection on incubation temperature, nesting behaviour and hatching success of common eiders (Somateria mollissima) in west Iceland

Incubating common eiders (Somateria mollissima) insulate their nests with down to maintain desirable heat and humidity for their eggs. Eiderdown has been collected by Icelandic farmers for centuries, and down is replaced by hay during collection. This study determined whether down collecting affected the female eiders or their hatching success. We compared the following variables between down and hay nests: incubation temperature in the nest, incubation constancy, recess frequency, recess duration, egg rotation and hatching success of the clutch. Temperature data loggers recorded nest temperatures from 3 June to 9 July 2006 in nests insulated with down (n = 12) and hay (n = 12). The mean incubation temperatures, 31.5 and 30.7°C, in down and hay nests, or the maximum and minimum temperatures, did not differ between nest types where hatching succeeded. Cooling rates in down, on average 0.34°C/min and hay nests 0.44°C/min, were similar during incubation recesses. Females left their nests 0–4 times every 24 h regardless of nest type, for a mean duration of 45 and 47.5 min in down and hay nests, respectively. The mean frequency of egg rotation, 13.9 and 15.3 times every 24 h, was similar between down and hay nests, respectively. Hatching success adjusted for clutch size was similar, 0.60 and 0.67 in down and hay nests. These findings indicate that nest down is not a critical factor for the incubating eider. Because of high effect sizes for cooling rate and hatching success, we hesitate to conclude that absolutely no effects exist. However, we conclude that delaying down collection until just before eggs hatch will minimize any possible effect of down collection on females.     

Polygyny in Willow Warblers <Emphasis Type="Italic">Phylloscopus trochilus</Emphasis> (Sylviidae,Passeriformes) in Middle European Russia: Differences in songs of polygynous and monogynous males

The study was performed in May to July of 1995 in Middle Russia (Skadovskii Zvenigorod Biostation, MSU, Moscow oblast: 55°44′ N, 36°51′ E). Monoterritorial polygyny was observed in one of seven studied Willow Warbler males Phylloscopus trochilus. The distance between the nests of the first and second females was 90 m. In the nest of the first female, five nestlings hatched on June 10 and the flight of the fledglings occurred on June 23. In the nest of the second female, a 5-to 6-day-old nestling of the cuckoo Cuculus canorus was found on June 18. The male actively participated in feeding the young in the first nest and did not participate in the feeding of the young in the second nest. The songs of the bigamous male differ significantly from the songs of monogamous males in the middle and final parts of the breeding cycle. The song of the bigamous male in the idle and end of the breeding season is similar to that in the beginning of the breeding season. Unmated males in the middle of the breeding season also retain a more permanent structure of their songs in comparison with breeding males. This case of polygyny seems to be related to special characteristics of the males such as their singing activity and the structure of their songs.     

Survival Response of <Emphasis Type="Italic">Bacteriovorax</Emphasis> in Surface Biofilm Versus Suspension when Stressed by Extremes in Environmental Conditions

The Bacteriovorax, previously in the genus Bdellovibrio, are prokaryotes that prey upon many Gram-negative bacteria. They are ubiquitous in salt-water environments and have been reported to have a strong association with biofilms. The purpose of this study was to test the hypothesis that this association affords protection for the Bacteriovorax and enhances their survival in nature when exposed to extreme environmental conditions. Experiments were designed to compare their survival in biofilms versus in suspension when exposed to extremes in salinity and temperature. Natural mixed-population biofilms generated in moderate-salinity (16‰) Patuxent River water and containing Bacteriovorax were exposed to drastic changes in salinity by placing in low-salinity (1‰) river water and salt-free (no measurable salinity) distilled water for up to 14 days. In a separate trial, the biofilm was exposed to extremes in temperature, 5°C and 35°C, for up to 12 weeks in aquarium mesocosms. Simultaneously, suspensions of the Bacteriovorax were exposed to the same extremes in salinity and temperature as biofilms. The results revealed that the Bacteriovorax typically were able to survive for a week or longer while in association with biofilms than when in suspension. These results are consistent with observations from nature and establish that biofilms are important in the survival and ecology of the Bacteriovorax.     

The aberrant stickleback Gasterosteus aculeatus in the Karlskrona archipelago, SE Sweden

The aberrant stickleback in the Karlskrona archipelago is probably a completely new form within the three‐spined stickleback Gasterosteus aculeatus complex. Males of this type differ from sympatric, normal stickleback males by being smaller and by having less striking nuptial coloration. They also build nests in algae above the bottom, whereas normal stickleback males build their nest at the bottom. Moreover, observations suggest that aberrant stickleback males have emancipated from most of the care of nest and offspring as they appear to transport fertilized eggs from the nest to the surroundings where they are left unattended. Whether this can be explained by sex‐specific reproductive strategies or by any other means is investigated. Preliminary results suggest the aberrant stickleback to be genetically distinct from regular morphs. The project will investigate this further and hopefully clarify whether the aberrant type has evolved in the Karlskrona archipelago, thus probably in sympatry with normal sticklebacks, or if it is of allopatric origin. With reproductively important morphological and behavioural deviations, our first guess would be that isolation is mediated through sexual selection. If this is true, isolation may have been relatively rapid making a sympatric origin less unlikely. The aberrant form is very rare and endangered. Presently, it is only found at two sites, both of which are threatened by an impending ferry terminal construction. A major aim of the project is to help preserve the aberrant stickleback. Most importantly, aberrants will be collected for captive breeding and introduction to new localities.     

Effects of ration and male density on the territoriality and nest-building of male three-spined sticklebacks (Gasterosteus aculeatus L.)

This study investigated the effects of food ration and male density on the territoriality and nest-building of sexually mature, male, three-spined sticklebacks. For a given density of males and when the food was distributed randomly throughout the area in which territories could be established, the proportion that established territories and built nests increased with ration. The proportion of males that held territories decreased with an increase in male density, while the rate at which nests were destroyed increased. When the food was distributed so that some males regularly obtained more food than others, these males tended to increase the size of their territories if they had built a nest. In the absence of a nest, territory size declined. It is suggested that high rations increased the resource holding power (RHP) of the males, while the presence of a nest increased the value of the territory to the occupier.     

Speciation in ninespine stickleback: reproductive isolation and phenotypic divergence among cryptic species of Japanese ninespine stickleback

Although similar patterns of phenotypic diversification are often observed in phylogenetically independent lineages, differences in the magnitude and direction of phenotypic divergence have been also observed among independent lineages, even when exposed to the same ecological gradients. The stickleback family is a good model with which to explore the ecological and genetic basis of parallel and nonparallel patterns of phenotypic evolution, because there are a variety of populations and species that are locally adapted to divergent environments. Although the patterns of phenotypic divergence as well as the genetic and ecological mechanisms have been well characterized in threespine sticklebacks, Gasterosteus aculeatus, we know little about the patterns of phenotypic diversification in other stickleback lineages. In eastern Hokkaido, Japan, there are three species of ninespine sticklebacks, Pungitius tymensis and the freshwater type and the brackish‐water type of the P. pungitius–P. sinensis species complex. They utilize divergent habitats along coast–stream gradients of rivers. Here, we investigated genetic, ecological and phenotypic divergence among three species of Japanese ninespine sticklebacks. Divergence in trophic morphology and salinity tolerance occurred in the direction predicted by the patterns observed in threespine sticklebacks. However, the patterns of divergence in armour plate were different from those previously found in threespine sticklebacks. Furthermore, the genetic basis of plate variation may differ from that in threespine sticklebacks. Because threespine sticklebacks are well‐established model for evolutionary research, the sympatric trio of ninespine sticklebacks will be an invaluable resource for ecological and genetic studies on both common and lineage‐specific patterns of phenotypic diversification.     

Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature‐dependent sex determination

Abstract The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature‐dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature‐dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg‐laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male‐male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male‐biased sex ratios, and that this provides an adaptive explanation for temperature‐dependent sex determination in A. muricatus.     

A MICROSATELLITE ASSESSMENT OF SNEAKED FERTILIZATIONS AND EGG THIEVERY IN THE FIFTEENSPINE STICKLEBACK

Attempts by males to steal fertilizations from other males are common in many species. In some sticklebacks, males also are known to steal eggs from the nests of rivals and to carry them back to their own nests. However the genetic consequences of these nest-raiding behaviors seldom have been investigated. Here we assess genetically the prevalence of sneaked fertilizations and egg stealing, and we describe the mating system in a natural population of the fifteenspine stickleback. Six microsatellite markers were developed and employed to assay a total of 1307 embryos from 28 nests. Guardian males and all nest-holding males in the local area also were genotyped for two to six loci Analysis of male genotypes and those of embryos revealed that five of the 28 nests (18%) contained progeny from sneaked fertilizations, and that four of the 24 nests (17%) with resident males contained stolen egg clutches Comparisons of the composite DNA genotypes of nest-holding males against those of inferred sneakers implicated one nest holder as the sneaker of a nest seven meters from his own. Also, the genetic data demonstrated that nests of males frequently contain eggs from multiple females. The multilocus genotypes of inferred mothers indicated that females mate with multiple males, sometimes over distances greater than one kilometer.     

Not all who wander are lost: nest fidelity in <Emphasis Type="Italic">Xylocopa virginica</Emphasis> examined by mark recapture

Relocation to novel nests (sometimes called drifting) in flying Hymenoptera is often interpreted as the result of navigation error and guard bees erroneously admitting foreign individuals into the nest. We studied nest fidelity and nest relocation of both females and males in a nesting aggregation of Xylocopa virginica in southern Ontario, Canada, where females can nest either solitarily or socially. Adult female and male bees were trapped at nest entrances, individually paint marked, and then released. Subsequent recapture patterns were used to assess nest fidelity: that is, how faithful individuals were to their home nest and how often they moved to another nest. Bees were considered to have relocated if they were recaptured in a nest different from the one in which they were initially trapped, indicating that they had spent at least one night in a new nest. Some females were only captured in one nest, some occasionally moved to new nests, temporarily or permanently, and a few were never caught in the same nest twice. In addition, females relocated to nests that were further away in 2007 when population density was low, suggesting that they seek out and claim nesting spaces when they are available. Males relocated more frequently than females, with most drifting from nest to nest in no obvious pattern. This indicates that males spend the night wherever space is available or in nests nearest to their territories. This study reveals that for both female and male X. virginica, nest membership is not as stable as once thought.     

Factors Influencing the Survival of Sympatric Gorilla (<Emphasis Type="Italic">Gorilla gorilla gorilla</Emphasis>) and Chimpanzee (<Emphasis Type="Italic">Pan troglodytes troglodytes</Emphasis>) Nests

Accurate and precise surveys of primate abundance provide the basis for understanding species ecology and essential information for conservation assessments. Owing to the elusive nature of wild apes and the vast region of dense forest they inhabit, population estimates of central chimpanzees (Pan troglodytes troglodytes) and western lowland gorillas (Gorilla gorilla gorilla) have largely relied on surveys of their nests. Specific information about the nesting behavior of apes permits the estimation of the number of nests built (nest creation rate). Similarly, information on nest characteristics and environmental factors can be used to estimate the time it takes nests to decay (nest decay rate). Nest creation and decay rates are then used to convert nest density estimates to absolute ape densities. Population estimates that use site-specific estimates of nest creation and decay rates are more accurate and precise. However, it is common practice to generalize these conversion factors across sites because of the additional cost of studies required to gather the information to estimate them. Over a 9-mo study period, we detected and monitored the time to decay of gorilla nests (N = 514) and chimpanzee nests (N = 521) in northern Republic of Congo. We investigated the influence of nest characteristics and environmental factors on nest survivorship and estimated the mean time to nest decay (or equivalently survival) using MARK. Key factors influencing nest decay rate included ape species, forest type, nest height, mean rainfall, nest structure, nest type, and primary aspects of nest construction. Our findings highlight the synergistic effect of behavior and environment on great ape nest degradation, as well as providing practical insights for improving measures to monitor remaining populations of these endangered species.     

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.