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.     

Male body size and brooding success under natural conditions in the freshwater Japanese goby, Rhinogobius sp. OR (orange type)

Males of the Japanese goby Rhinogobius sp. OR (orange type) establish nests under stones in streams. They provide care to egg masses until hatching. We carried out field observations and a field experiment in a natural stream to examine the effect of male body size on brooding success. An experiment excluding guarding males indicated that their presence has a positive effect on nest defense. Field data showed that male body size was positively correlated with the size of the egg mass that was initially found at the nest. Furthermore, a sequential increase in egg mass size seen in the nests of larger males indicated that multiple females spawned during a single breeding cycle of larger males. To examine male brooding success, two dependent variables, egg mass persistence (days from initial egg mass to disappearance or hatching) and hatching success were analyzed. The results indicated that the variation found in both dependent variables was significantly explained by two independent variables, namely, initial egg-mass size and the number of matings. It is also suggested that male body size indirectly influenced brooding success through positive correlations with these independent variables.     

Variation in male mating success in the paternal nest brooder, Rhinogobius goby, along a river course

Rhinogobius sp. CB (cross band type) is an amphidromous freshwater goby which receives paternal nest care under stones on river beds. This goby is known to migrate to the upper reaches of rivers as it grows. In the present study, the relationships among male mating success of Rhinogobius sp. CB, male body size, the size frequency distribution of river bed stones and the presence of the sympatric goby Tridentiger brevispinis (which uses nest sites similar to those of Rhinogobius sp. CB) were investigated along the course of the Aizu River, Wakayama Prefecture, Japan. In the lower reach, where T. brevispinis was present and large stones were scarce, the sizes of the nest stones and the egg clusters of male Rhinogobius sp. CB were smaller than those of T. brevispinis. In the middle and the upper reaches, where T. brevispinis was absent and large stones were abundant, males of Rhinogobius sp. CB used larger nest stones than in the lower reach. In both gobies, there were positive correlations among male body size, nest size and egg cluster size in all reaches. Nest-choice experiments carried out in the laboratory, with or without a rival, showed that males of both gobies preferentially used large nest sites and that large males had an advantage in male-male competition for large nest sites. These results indicate that large male body size can increase male mating success and that male mating success increases in the upper reach in this goby. The migration pattern of Rhinogobius sp. CB was also discussed in relation to these findings.     

Selection of sites for egg deposition and spawning dynamics in the waccamaw darter

Synopsis We provided 93 experimental spawning covers for the waccamaw darter. We grouped the covers (3 sizes of slate and one of concave tile) in three arrangements at six Lake Waccamaw locations to separate the variables of water depth, distance from shore, cover density and cover type. Tag returns of marked males suggest low fidelity for nest sites. Egg production under the 3 different sizes of slate was not significantly different. Egg production under the tile was significantly less than that under the slates. Egg production was significantly higher off the undeveloped southeastern shore in 2 m of water and lowest at the shallowest location with the highest experimental cover density. The number of eggs in nest is positively correlated with male size. We conclude that medium size slate covers placed in a linear arrangement in 2 m of water on a mixed sand bottom result in the highest egg production for the waccamaw darter.     

Feeding ecology of the American freshwater goby Ctenogobius shufeldti (Gobiidae, Perciformes) in a sub-tropical estuary

The feeding ecology of the American freshwater goby Ctenogobius shufeldti in a low salinity salt-marsh habitat in the Paranaguá Bay estuarine complex (Brazil) was assessed through the gut analysis of 632 individuals. The effects of a set of abiotic factors (type of sediment, salinity, temperature and estuarine reach), season and body size on dietary composition were analysed. Seasonal and size-related changes in feeding strategy, feeding intensity and trophic level were assessed. The effects of gape and body size on prey size use were also analysed. The results showed that C. shufeldti is a typical omnivorous, generalized benthic predator of low trophic levels throughout the seasons and size classes, feeding on 56 dietary items; tanaids, chlorophyte algae, ostracods, gastropods, detritus and benthic diatoms made up the bulk of its diet. The tanaid Kalliapseudes schubarti was the main prey item in both numerical and volumetric terms. The gut fullness was persistently high across the seasons. As expected for a typical generalized, opportunistic omnivorous feeder: (1) seasonal and spatial-temporal variability of abiotic factors had a significant effect on diet structure, (2) season accounted for most of the dietary variation and (3) diet composition and the size of prey consumed did not vary across the size classes.     

Length and sequence variation in the mitochondrialDNA control region of the Etruscan freshwater goby Padogobius nigricans (Teleostei, Gobiidae)

The primary structures of the mtDNA control region, the flanking tRNA^Pro and tRNA^Phe genes and the partial 12S rRNA gene of the freshwater Etruscan goby Padogobius nigricans (Teleostei, Gobiidae) were determined. A tandem array of variable 17-bp repeats, named R1–7, was found to be responsible for most of the observed length and sequence variation between individuals.     

Correlates of male mating success in two natural populations of the damselfly lschnura graellsii (Odonata: Coenagrionidae)

Abstract.

• 1 Two natural populations of Ischnura graellsii were studied in north-west Spain by means of mark-release-recapture techniques. Recaptured males were a random sample of the original marked population with regard to date of marking. At O Rosal a greater proportion of young males than old males disappeared after marking; at Lourizán recaptured males were larger than unrecaptured ones.
• 2 The number of matings observed in both populations showed great daily variation. Most of the variation is accounted for by climatic variables. Most males (56–65%) and many females (41–45%) were never observed to mate.
• 3 Male LMS was highly correlated with lifespan in both populations. At O Rosal, male LMS was also positively correlated with body length, and mated males were larger than unmated males. This surprising result for a non-territorial species was due to the positive correlation between date of marking and size. There was a positive correlation between body size and mobility for males at O Rosal, but mobility was not correlated with male LMS.
• 4 As predicted by sexual selection theory, the standardized variance in male LMS was greater than in female LMS. Variation in mature lifespan explained 16% of variance in male LMS at Lourizán and 28% at O Rosal.

     

Body size,male aggression,and male mating success in the cottonwood borer,Plectrodera scalator (Coleoptera: Cerambycidae)

The natural history and mating system ofPlectrodera scalator exhibit several unusual characteristics. Larvae and adults feed on the wood and foliage, respectively, of the same plant,Populus deltoides. The population sex ratio, based on censuses of oviposition areas, is female-biased. Females are significantly larger than males, yet males are intensely aggressive. Larger males tend to win escalated battles, which involve grasping of antennae with mandibles, but smaller males can defeat larger males if they grasp their opponent's antenna first. Most escalated fights involve possession of a female, but prior possession does not play a role in determining the outcome of these fights. The size-dependent fighting advantage does not translate into a mating advantage for larger males. There is no significant difference in elytron length or body mass between mating and single males. Larger females are not preferred as mates. The mating system appears to be a mixture of female-defense and scramble-competition tactics. One advantage to males of aggression may be in its effect on sperm precedence. Males appear to be able to remove previously deposited sperm from a female's reproductive tract.     

Substratum as a factor in the distribution of two prosobranch freshwater snails,Viviparus bengalensis and Melania scabra

Laboratory experiments were conducted to ascertain the substratum preferendum of Viviparus bengalensis and Melania scabra. When the food (Spirogyra) was offered both on stones and sand, the average distribution of V. bengalensis and M. scabra was 19% and 10% on stone and 52% and 80% on sand respectively. In the absence of food from both stone and sand and also when sand alone was baited, both snails flocked principally towards sand. When stone alone was provided with food, V. bengalensis and M. scabra displayed 16% and 15% distribution on stone and 49% and 45% on sand respectively. Ecological significance of these results is discussed.     

The effects of male body size on territorial and mating success in the landmark-defending fly Hermetia comstocki (Stratiomyidae)

Abstract.

• 1 Males of Hermetia comstocki Williston compete for territorial control of certain agaves and yuccas. Winners copulate with females that visit these plants solely to acquire a mate.
• 2 Males vary in body weight by more than an order of magnitude and larger flies almost always defeat smaller ones in aerial contests for control of landmark territories.
• 3 The mean body size (as measured by wing-length) was significantly greater for males retaining residency at a site for at least one hour compared to males unable to do so. Likewise, males able to return to a perch site in the study area on more than one day were larger on average than males unable to do so.
• 4 Male preferences for landmark territories remained similar across years. Large males dominated the perch landmarks most likely to be occupied by males and most likely to be visited by females.
• 5 Despite the fighting and territorial advantages enjoyed by large males, the mean size of males found mating with females was not significantly larger than that of the general population.
• 6 The apparent failure of large males to secure a statistically significant mating advantage may be a statistical consequence of the small sample size of males observed mating. On the other hand, any mating advantage of large males may be reduced because (a) receptive females visit many different landmarks, (b) females mate with the first male they encounter at a landmark, regardless of his size, (c) there are usually many vacant landmarks available for smaller males, and (d) even popular territories are often open to small males, thanks to the low site-tenacity of territory owners.

     

Effect of clutch size on male egg-fanning behavior and hatching success in the goby, Eviota prasina (Klunzinger)

In fish that exhibit paternal care, the females often choose their mates on the basis of male traits that are indicative of the parental ability of the males. In a marine goby, Eviota prasina, males tend their eggs within their nests until hatching, and females prefer males that have longer dorsal fins and exhibit courtship behavior with a higher frequency as their mates. In order to clarify the relationship between these sexually selected traits and the parental ability of males of E. prasina, the factors affecting the hatching success of eggs within male nests and the male parental care behavior were examined in an aquarium experiment. Females spawned their eggs in male nests and the clutch size of females showed a high individual variation (range = 88-833 eggs). The hatching success of eggs within male nests showed a positive correlation with the time spent by males in fanning eggs and the clutch size. In contrast to the prediction, however, the hatching success did not show a significant correlation with the sexually selected traits, i.e., the male dorsal fin length and the frequency of courtship displays. Moreover, multiple regression analysis indicated that the time spent by the males in fanning was the most important factor affecting the survival rate of the eggs. The time spent by males in fanning behavior was influenced by the clutch size within their nests; the fanning behavior of males occurred with a higher frequency when they tended larger clutches. Males are required to invest a greater effort in egg-tending behavior to achieve a higher hatching success when they receive larger clutches, probably due to the greater reward for their parental behavior. Based on their mate choice, females may obtain other benefits such as high quality offspring.     

Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations

Polar bears (Ursus maritimus) have experienced substantial changes in the seasonal availability of sea ice habitat in parts of their range, including the Beaufort, Chukchi, and Bering Seas. In this study, we compared the body size, condition, and recruitment of polar bears captured in the Chukchi and Bering Seas (CS) between two periods (1986–1994 and 2008–2011) when declines in sea ice habitat occurred. In addition, we compared metrics for the CS population 2008–2011 with those of the adjacent southern Beaufort Sea (SB) population where loss in sea ice habitat has been associated with declines in body condition, size, recruitment, and survival. We evaluated how variation in body condition and recruitment were related to feeding ecology. Comparing habitat conditions between populations, there were twice as many reduced ice days over continental shelf waters per year during 2008–2011 in the SB than in the CS. CS polar bears were larger and in better condition, and appeared to have higher reproduction than SB bears. Although SB and CS bears had similar diets, twice as many bears were fasting in spring in the SB than in the CS. Between 1986–1994 and 2008–2011, body size, condition, and recruitment indices in the CS were not reduced despite a 44‐day increase in the number of reduced ice days. Bears in the CS exhibited large body size, good body condition, and high indices of recruitment compared to most other populations measured to date. Higher biological productivity and prey availability in the CS relative to the SB, and a shorter recent history of reduced sea ice habitat, may explain the maintenance of condition and recruitment of CS bears. Geographic differences in the response of polar bears to climate change are relevant to range‐wide forecasts for this and other ice‐dependent species.     

水位对黑斑侧褶蛙蝌蚪形态表型、 白细胞数量和应激反应的影响

为探究水位变化对黑斑侧褶蛙（Pelophylaxnigromaculatus）蝌蚪形态表型、免疫功能和应激反应能力的影响,实验室内测定了水位恒定组以及水位快速、中速和慢速下降组37期蝌蚪发育至变态完成期的变态时长、身体大小和血液中各型白细胞的百分比,以及嗜中性粒细胞与淋巴细胞比值的变化。结果表明,水位快速下降显著缩短了蝌蚪的变态时长（P <0.05）,体长下降明显（P <0.05）,体重和体宽有所降低,但组间差异不显著（P> 0.05）。嗜中性粒细胞的百分比快速下降组显著高于其他处理组,单核细胞的百分比水位恒定组显著高于中速下降组（P <0.05）,嗜酸性粒细胞、嗜碱性粒细胞和淋巴细胞的百分比均无明显的组间差异（P>0.05）;嗜中性粒细胞与淋巴细胞比值快速下降组显著高于其他处理组（P <0.05）。水位加速下降导致登陆后幼蛙的个体变小,由嗜中性粒细胞和单核细胞所代表的天然免疫能力变化趋势不同,应激反应能力增强,可能不利于幼蛙的存活。     

Spatial and temporal variations in nesting success and the causes of nest losses of the freshwater three-spined stickleback,Gasterosteus aculeatus

Synopsis Two experients were conducted to determine the effect of male color phenotype present during development on the mate choice of adult female guppies. Females were raised with either a colorful male, non-colorful male, or no male, and then measured for choice of a colorful or non-colorful male in a two-stimulus visual choice test. In the first experiment, adult females were measured for choice between the same male phenotypes used during the developmental exposure. Females raised with colorful males had significantly higher choice scores for colorful males than did females raised with non-colorful males or with no male. In the second experiment, an effect of developmental experience was observed when adult females were tested for choice with a general range of colorful and non-colorful males. However, this effect of experience during development was not detected when females were tested for choice between the same male phenotypes used during the developmental exposure. The predation regime of the source population, either high or low, showed no consistent effect on average female choice or on whether developmental experience changed female mate choice. Overall, these experiments show that experience with male phenotypes can affect the mate choice of adult guppies, but this effect was not observed under all developmental treatments or test conditions. Such an effect could significantly change the dynamics of the evolution of female preference due to sexual selection in the guppy.     

Differential modes of selection on the rhodopsin gene in coastal Baltic and North Sea populations of the sand goby,Pomatoschistus minutus

An excellent model to elucidate the mechanisms and importance of evolution in the marine environment is the spectral tuning mechanism of the visual pigment in vertebrates. In the sand goby Pomatoschistus minutus (Teleostei; Gobiidae), a distribution‐wide study showed that spatial variation at the rhodopsin gene (RH1) matches the characteristics of specific light environments. This match suggests that populations are locally adapted to selective light regimes targeting the RH1 gene. If so, then the direction of selection should depend on the regional spatial and temporal stability of the light conditions. We tested this prediction by comparing goby populations from two regions: the Baltic Sea, characterized by divergent, but temporally stable light conditions, and the North Sea, characterized by locally heterogeneous and temporally variable light conditions. RH1 sequences of 491 Pomatoschistus minutus individuals from 15 locations were analysed. We found that variation at the RH1 gene in the Baltic populations showed signatures of diversifying selection, whereas the RH1 gene in the North Sea showed signatures of stabilizing selection. These different modes of selection are consistent with the regional light conditions and hence support our predictions, but may also be influenced by migration between the open sea and more turbid estuarine environments. An interesting observation is that within one gene, synonymous and non‐synonymous SNPs show a totally different pattern between populations. Population differentiation based on non‐synonymous SNPs of the RH1 gene correlated with spectral variation of the local environment of the sand goby populations. In contrast, the differentiation based on synonymous SNPs of RH1 reflects more the neutral historical pattern of the species.     

Correlates of male quality in the field cricket, Gryllus campestris L.: age, size, and symmetry determine pairing success in field populations

Sexual selection in field crickets (Gryllidae) is well documented.Several studies have identified male traits, such as age andbody size, that influence pairing success in the field. HereI show how these traits covary with male quality by examiningthe degree of fluctuating asymmetry in male Gryllus campestris.Older males were both larger and more symmetrical. Principalcomponents analysis suggests that these three variables wereessentially measures of the same trait, male quality. A comparisonof paired and calling males showed that males of high qualitywere more successful in obtaining mates; paired males were older,larger, and more symmetrical. The area of the harp covariedwith morphological traits and determined the carrier frequencyof the male's call. Information related to male quality wastherefore available for female discrimination.     

Flight dimorphism is related to survival,reproduction and mating success in the leaf beetle Oreina cacaliae

1. Alternative life histories may be maintained in populations due to variation in the costs and benefits of the underlying strategies. In this study, potential costs of dispersal by flight were investigated as an alternative life‐history strategy in the mountain‐living chrysomelid beetle Oreina cacaliae. 2. In this species, previous mark–recapture studies showed a dispersal dimorphism in both males and females. While a fraction of the population engages in flight in autumn and spring (in the following referred to as ‘flyers’), the other part does not fly (non‐flyers). Flyers emerge earlier than non‐flyers and feed on a spring host plant before the emergence of the main host plant. 3. In this study, the overwintering and dispersal locations were recorded over 7 years in the field, flyers from the spring host plant were collected, and morphology and lifetime reproductive output and survival of collected flyers and non‐flyers were compared. 4. A potential trade‐off between flight and life‐history traits was observed: flyers were smaller in size, lighter in body mass, had a lower lifetime fecundity and a higher mortality. 5. Mating experiments of field‐caught beetles in the laboratory showed that larger beetles had a higher (multiple) mating success, but there was no evidence for size‐assortative mating. It is hypothesized that one reason for small beetles to disperse by flight might be to escape competition for mates with larger non‐flyers. 6. The overwhelming quantity of beetles found on the spring host every year reveals that the flying strategy is successful, despite the costs and risks.     

Effects of a low oxygen environment on parental effort and filial cannibalism in the male sand goby, Pomatoschistus minutus

In fish, brood cycling parental males sometimes eat some orall of their eggs, a behavior termed filial cannibalism. Wetested predictions of filial cannibalism models related to thecost of parental care in the male sand goby, Pomatoschistusminutus, by increasing the parental effort (fanning expenditure)through reduced levels of dissolved oxygen to 39% in an experimentalgroup, whereas a control group had fully saturated water. Malesshowed both full-clutch cannibalism and partial-clutch cannibalismin both treatments. Giving the males one to three females tospawn with, we found that small clutches were completely eatenmore often than were larger ones, whereas partial-clutch cannibalismwas not affected by clutch size. Although treatment did notaffect filial cannibalism, it did affect a male's energy statesuch that males in the low oxygen treatment lost more body fat,indicating a greater fanning effort. This shows that males inthe low oxygen treatment allocated more energy to the presentbrood, potentially at the expense of future reproductive success.Our study strongly suggests that filial cannibalism in malesand gobies represents a strategic life-history decision asan investment in future reproductive success, and is not triggeredby a proximate need for food necessary for the male's own survival.Furthermore, males in the low oxygen treatment built nests withlarger entrances, and were less likely to rebuild their nestsafter destruction. Presumably, this makes fanning easier butthe nest more vulnerable to predators, suggesting a trade-offbetween fanning and nest defense.