Size-dependent precopulatory behavior as mate-securing tactic in the Japanese stag beetle, Prosopocoilus inclinatus (Coleoptera; Lucanidae)

Males of the Japanese stag beetle Prosopocoilus inclinatus show dimorphism in body size. Since females frequently resist male courtship behavior, males often fail to mate after encounters with females. The males of two morphs showed different precopulatory behavior. During encounters with females, small males acted more persistently against females resistance than large males by grasping the female more solidly and as a result, succeeded in copulation more frequently. This persistent precopulatory behavior could be regarded as an alternative mating tactic of small males that are inferior to large males in direct physical competition.     

Condition‐dependent ejaculate production affects male mating behavior in the common bedbug Cimex lectularius

Food availability in the environment is often low and variable, constraining organisms in their resource allocation to different life‐history traits. For example, variation in food availability is likely to induce condition‐dependent investment in reproduction. Further, diet has been shown to affect ejaculate size, composition and quality. How these effects translate into male reproductive success or change male mating behavior is still largely unknown. Here, we concentrated on the effect of meal size on ejaculate production, male reproductive success and mating behavior in the common bedbug Cimex lectularius. We analyzed the production of sperm and seminal fluid within three different feeding regimes in six different populations. Males receiving large meals produced significantly more sperm and seminal fluid than males receiving small meals or no meals at all. While such condition‐dependent ejaculate production did not affect the number of offspring produced after a single mating, food‐restricted males could perform significantly fewer matings than fully fed males. Therefore, in a multiple mating context food‐restricted males paid a fitness cost and might have to adjust their mating strategy according to the ejaculate available to them. Our results indicate that meal size has no direct effect on ejaculate quality, but food availability forces a condition‐dependent mating rate on males. Environmental variation translating into variation in male reproductive traits reveals that natural selection can interact with sexual selection and shape reproductive traits. As males can modulate their ejaculate size depending on the mating situation, future studies are needed to elucidate whether environmental variation affecting the amount of ejaculate available might induce different mating strategies.     

The relative influence of prior residency and dominance on the early feeding behaviour of juvenile Atlantic salmon

In many species where social hierarchy mediates conflict over resources, dominant individuals monopolize food, shelter and reproductive opportunities. The benefits of social dominance, however, can often be offset by a prior residence advantage, whereby individuals arriving first in a new habitat obtain, and subsequently defend, the most profitable sites. We investigated the relative influence of these two factors on the acquisition of feeding territories by juvenile Atlantic salmon,Salmo salar L., by placing groups of six individuals of known dominance rank sequentially into an experimental arena with feeding sites of varying quality. Dominants had an advantage over subordinates in the percentage of time spent in a good-quality feeding site and individual feeding rate. There was also a significant time of arrival effect: those individuals that arrived first in a habitat monopolized the resource. The two effects were of approximately equal strength, so that late-arriving dominant fish had similar success as prior resident subordinates. These results indicate that both dominance and prior residence are important in the feeding behaviour of juvenile Atlantic salmon, and that the two factors can have independent and additive effects.Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

You Are What You Eat: Food Limitation Affects Reproductive Fitness in a Sexually Cannibalistic Praying Mantid

Resource limitation during the juvenile stages frequently results in developmental delays and reduced size at maturity, and dietary restriction during adulthood can affect longevity and reproductive output. Variation in food intake can also result in alteration to the normal pattern of resource allocation among body parts or life-history stages. My primary aim in this study was to determine how varying juvenile and/or adult feeding regimes affect particular female and male traits in the sexually cannibalistic praying mantid Pseudomantis albofimbriata. Praying mantids are sit-and-wait predators whose resource intake can vary dramatically depending on environmental conditions within and across seasons, making them useful for studying the effects of feeding regime on various facets of reproductive fitness. In this study, there was a significant trend/difference in development and morphology for males and females as a result of juvenile feeding treatment, however, its effect on the fitness components measured for males was much greater than on those measured for females. Food-limited males were less likely to find a female during field enclosure experiments and smaller males were slower at finding a female in field-based experiments, providing some of the first empirical evidence of a large male size advantage for scrambling males. Only adult food limitation affected female fecundity, and the ability of a female to chemically attract males was also most notably affected by adult feeding regime (although juvenile food limitation did play a role). Furthermore, the significant difference/trend in all male traits and the lack of difference in male trait ratios between treatments suggests a proportional distribution of resources and, therefore, no trait conservation by food-limited males. This study provides evidence that males and females are under different selective pressures with respect to resource acquisition and is also one of very few to show an effect of juvenile food quantity on adult reproductive fitness in a hemimetabolous insect.     

Predicting the Competitive Regime of Female <Emphasis Type="Italic">Colobus vellerosus</Emphasis> from the Distribution of Food Resources

We examined the spatial and temporal distribution of the foods of ursine colobus (Colobus vellerosus) at Boabeng-Fiema, Ghana as a means to predict the monopolizablity and usurpability of their food resources. Recent evidence suggests that food may not be limiting for folivorous primates, and that male sexual coercion may be a more important influence on folivore social organization. To address the question, we collected focal data on the feeding behavior of adult females and males over 11 mo (September 2000-August 2001) on 2 groups: WW (n = 31–33 individuals) and B (n = 8–16 individuals). We also conducted phenological monitoring and a tree survey of the two-group home ranges to establish food availability and distribution. We used 2 behavioral or organism-defined indicators of feeding behavior to assess potential resource contestability: food site residence time and distance moved between food sites. The colobus fed on a high diversity of species, most of their food trees were not clumped in distribution, within-tree interfood distances were short, and food trees were large. The only condition associated with the potential for monopolization was low food tree density. However, low food tree density may be offset by the colobus’ use of large trees. Taken together, the ecological and behavioral indicators suggest the food resources of Colobus vellerosus had a low potential for monopolization. Our results also indicate mature leaves had the longest food site residence time, which may suggest they should be the most usurpable plant part, though their presumed low quality and high abundance probably counteracted the effect. The pattern implied the potential for direct feeding competition among Colobus vellerosus at Boabeng-Fiema was low and agonistic interactions over food are not expected. Instead, a group size effect on feeding efficiency should be a more predominant influence on feeding efficiency, if food is limiting for the species.     

Shelter competition between resident male red swamp crayfish Procambarus clarkii (Girard) and conspecific intruders varying by sex and reproductive status

The shelter defense dynamics of reproductively active (Form I) male red swamp crayfish Procambarus clarkii (Girard) were investigated by staging serial intrusions by male, maternal or non-maternal female conspecifics after one day of residence. The male residents showed a direct contest advantage only against non-maternal females, and won a significantly higher proportion of the encounters against non-maternal females than against either male or maternal female intruders. However, there was no significant difference in success against male or maternal female intruders. Further experiments against male intruders showed that increasing male prior residence to either 2 or 4 days did not significantly improve the residents’ proportion of successful encounters. A final experiment revealed extremely low shelter fidelity in male P. clarkii, the most likely reason why male shelter defense against conspecific males and maternal females is not successful. These results, combined with those of past research, suggest that non-maternal females, juveniles and recently molted conspecifics are most vulnerable to predation and cannibalism, since males and maternal females easily out-compete non-maternal females for shelter, and adults out-compete juveniles. These findings may have implications for P. clarkii aquaculture and general management.     

Interspecific relationship between the Japanese horned beetle and two Japanese stag beetle species

The Japanese horned beetle Trypoxylus dichotomus septentrionalis and the Japanese stag beetles Lucanus maculifemoratus maculifemoratus and Prosopocoilus inclinatus inclinatus generally occur syntopically and aggregate on oak tree surfaces that exude sap. Securement of these sap sites might be directly linked to male reproductive success. Among the three species, it is likely that males of T. d. septentrionalis are dominant in occupation of feeding sites because of their larger body size. However, there is no clear evidence of this superiority. Moreover, if T. d. septentrionalis is dominant, the mechanism by which the two stag beetle species secure the feeding sites remains unclear. In the present study, I used body mass to compare the body size among males of T. d. septentrionalis, L. m. maculifemoratus and P. i. inclinatus. Further, to clarify the interspecific relationship between the horned beetle and the two stag beetles, I investigated the seasonality of emergence pattern of males at the feeding sites in the field. Comparison of body mass and observation of fighting behavior revealed that males of T. d. septentrionalis have an apparent superiority over males of the two stag beetle species. The seasonal emergence patterns of the two stag beetle species at the feeding sites showed bimodal distributions, and avoided the peak of emergence in T. d. septentrionalis. My results suggest that the two stag beetle species exhibit mate‐securing tactics by emerging at the feeding sites early and late during the breeding season, in order to avoid encountering T. d. septentrionalis.     

Shelter competition between resident male red swamp crayfish Procambarus clarkii (Girard) and conspecific intruders varying by sex and reproductive status

The shelter defense dynamics of reproductively active (Form I) male red swamp crayfish Procambarus clarkii (Girard) were investigated by staging serial intrusions by male, maternal or non-maternal female conspecifics after one day of residence. The male residents showed a direct contest advantage only against non-maternal females, and won a significantly higher proportion of the encounters against non-maternal females than against either male or maternal female intruders. However, there was no significant difference in success against male or maternal female intruders. Further experiments against male intruders showed that increasing male prior residence to either 2 or 4 days did not significantly improve the residents' proportion of successful encounters. A final experiment revealed extremely low shelter fidelity in male P. clarkii, the most likely reason why male shelter defense against conspecific males and maternal females is not successful. These results, combined with those of past research, suggest that non-maternal females, juveniles and recently molted conspecifics are most vulnerable to predation and cannibalism, since males and maternal females easily out-compete non-maternal females for shelter, and adults out-compete juveniles. These findings may have implications for P. clarkii aquaculture and general management.     

Fighting Strategies in Crayfish Orconectes rusticus (Decapoda, Cambaridae) Differ with Hunger State and the Presence of Food Cues

Crayfish, bearing dangerous weapons in the form of chelae, resolve intraspecific conflicts using stereotyped behaviors and structured, escalated encounters. According to predictions of game theory models, any decision to resort to unrestrained combat without prior careful behavioral assessment of the opponent's fighting abilities carries great risks. The present study examines the significance of internal hunger states and the presence of chemical food cues in this decision process using a 2 × 2 factorial design. Hungry crayfish escalated more rapidly, and thus took greater risks, during agonistic encounters, while the presence of a food source reduced the rate at which fights increased in intensity. However, there were no significant differences in fighting behavior as a result of the interaction between these two variables. We then address the complex trade-offs that individuals face in fighting with respect to increased risks of injury, appetitive states, and opportunities for resource access.     

Contrasting phenotypic correlations in food provision of male Tengmalm's owls (Aegolius funereus) in a temporally heterogenous environment

Summary We examined the food provision rate of male Tengmalm's owls,Aegolius funereus, during one 3 year vole cycle consisting of consecutive low, increase and peake vole years. The data were collected in the midnestling period when males provisioned the whole family. In the low vole year, males with a low loading index (g/cm²) of flying area fed their offspring more often than did males with a high loading index, whereas in the peak vole year the opposite trend was evident. Similar relationships were found in the food mass provisioned to the nest. In the increase vole year, male body size had no effect on feeding efficiency. In the peak vole year, when large voles are abundant, heavy males preyed on larger voles than were generally available in their territories, indicating that largeness may increase strike power in hunting attempts. In the low vole year, when breeding is costly due to food scarcity and extensive hunting area, small males are more economical fliers and efficient hunters than large males. The contrasting trends in correlations between male size and feeding efficiency in years of vole abundance versus scarcity suggest that no fixed phenotype may most efficiently cope with variable food supply.     

Agonistic interactions between nymphs of Lycorma delicatula (Hemiptera: Fulgoridae)

The nymphs of Lycorma delicatula typically aggregate on tree branches for feeding. We studied agonistic interactions between nymphs in the field and investigated the effects of prior residence and body size on contest outcome. Resident nymphs maintained positions on tree branches and engaged in feeding, whereas intruding nymphs moved along tree branches. When an intruder approached, the resident typically raised its front legs as a threat posture. The intruder would either move away or palpate the resident, and the resident often lowered its body when palpated. The intruder would then attempt to shake the resident back and forth, with the number of attempts varying from one to several. The resident either maintained its position or fled. After a contest, the winner was determined to be the one occupying the contested position on the branch. The resident nymphs won 84.2% of the agonistic encounters, and the nymphs with larger body size won 63.2% of the agonistic encounters. Logistic regression analysis revealed that prior residence was a significant factor for the contest outcome, but body size was not. We discuss the hypotheses for the dominance of the residents in agonistic interactions between nymphs of L. delicatula.     

Feeding territoriality and the reproductive consequences in brown skuas<Emphasis Type="Italic"> Catharacta antarctica lonnbergi</Emphasis>

In the maritime Antarctic, brown skuas (Catharacta antarctica lonnbergi) show two foraging strategies: some pairs occupy feeding territories in penguin colonies, while others can only feed in unoccupied areas of a penguin colony without defending a feeding territory. One-third of the studied breeding skua population in the South Shetlands occupied territories of varying size (48 to >3,000 penguin nests) and monopolised 93% of all penguin nests in sub-colonies. Skuas without feeding territories foraged in only 7% of penguin sub-colonies and in part of the main colony. Females owning feeding territories were larger in body size than females without feeding territories; no differences in size were found in males. Territory holders permanently controlled their resources but defence power diminished towards the end of the reproductive season. Territory ownership guaranteed sufficient food supply and led to a 5.5 days earlier egg-laying and chick-hatching. Short distances between nest and foraging site allowed territorial pairs a higher nest-attendance rate such that their chicks survived better (71%) than chicks from skua pairs without feeding territories (45%). Due to lower hatching success in territorial pairs, no difference in breeding success of pairs with and without feeding territories was found in 3 years. We conclude that skuas owning feeding territories in penguin colonies benefit from the predictable and stable food resource by an earlier termination of the annual breeding cycle and higher offspring survivorship.Research licence: Umweltbundesamt Bonn 13.4-94003-1/5-7.     

Territorial defence of space and feeding sites by a plethodontid salamander

Two series of experiments were conducted, one in field enclosures and another in the laboratory, to test the hypothesis that the salamander Desmognathus monticola (family Plethodontidae) defends its refuges and feeding sites against conspecific intruders. When two identical cover sites were provided as refuges in the laboratory, residents and intruders occupied separate cover sites significantly more often than the same sites. Residents did not, however, show strong preference for the same site, nor did they consistently defend a specific site. When food supplements were provided consistently at the same cover sites in field enclosures, resident D. monticola occupied and defended the feeding sites significantly more frequently against intruders than the non-feeding cover sites. Individuals not receiving food supplements also excluded intruders from the occupied cover sites but did not defend a specific cover site. Residents in enclosures where no food supplements were provided were significantly more active at night, outside cover sites, than residents receiving food supplements. Individual D. monticola exhibit territoriality by excluding intruders from the refuges they occupy. Providing food supplements increases the site specificity of individuals and decreases the amount of time spent in nocturnal activity.     

Spatial distribution patterns of sheep following manipulation of feeding motivation and food availability

We hypothesised that (i) increased feeding motivation will cause sheep to move further apart as a result of individuals trying to find food and (ii) in conditions of high food availability, sheep will move less and show greater social attraction. The effects of both feeding motivation and food availability on spatial distribution was examined in eight groups of food-deprived (high feeding motivation) and satiated (low feeding motivation) sheep in good or poor food resource plots in a 2 × 2 design. Distance travelled was assessed using Global Positioning System collars, grazing time using scan sampling and social cohesion using proximity collars that record the number and duration of encounters within 4 m. Food-deprived sheep in the good-resource plots grazed the most, whereas satiated sheep in the poor-resource plots grazed the least (P = 0.004). Food deprivation had no significant effect on the number or duration of encounters and feeding motivation appeared to have little effect on spatial distribution. Contrary to expectation, sheep had more encounters (P = 0.04) of a longer total duration (P = 0.02) in poor-resource plots than in good-resource plots, indicating that sheep were showing more social cohesion if food was scarce. Our findings suggest that when food is scarce, animals may come together in an attempt to share information on food availability. However, when a highly preferred food is abundant and well dispersed, they may move apart in order to maximise the intake. It is concluded that the particular details of our experiment, namely the even distribution or absence of a highly preferred food, affected spatial distribution patterns as sheep tried to find this food and maximise the intake.     

Food patch structure and plant resource partitioning in interspecific associations of amazonian tamarins

ávila-Pires’ saddle-back tamarins (Saguinus fuscicollis avilapiresi) and red-cap moustached tamarins (S. mystax pileatus), coexisting in highly stable mixed-species groups, overlapped considerably in their use of plant food resources at an Amazonian terra firme forest site. Overlap between food types consumed by the two species was particularly high during periods of lowest fruit availability, when they resorted to a common food supply, primarily the pod exudates of two emergent species of legume trees (Parkia nitida andParkia pendula) and nectar ofSymphonia globulifera. Within-group interspecific competition did not covary with independent measures of resource availability, contrary to predictions based on resource partitioning models. A greater number of both saddle-back and moustached tamarins were able to feed for longer patch residence periods within larger and more productive food patches, whereas small and clumped patches could be monopolized by the socially and numerically dominant moustached tamarins to the physical exclusion of the smaller-bodied saddle-back tamarins. Overall rates of interspecific aggression were extremely low, however, partly because patches that could be monopolized contributed with a minor proportion of either species’ diet. Saddle-backs foraged at lower levels in the understory and encountered smaller food patches more often, whereas moustached tamarins foraged higher and encountered more larger patches in the middle canopy. Although the two species led one another to differently-sized patches, moustached tamarins initiated most feeding bouts and encountered significantly larger and more productive patches that tended to accommodate the entire mixed-species group. Disadvantages of exploitative and interference feeding competition over plant resources, and advantages of shared knowledge of food patches, are but one component of the overall cost-benefit relationship of interspecific associations in tamarins.     

Spatial Dispersion and Nonmigratory Spawning in the Bluehead Wrasse (Thalassoma bifasciatum)

Earlier studies of the behavior of the bluehead wrasse Thalassoma bifasciatum have shown it to be a migratory spawner with large terminal-phase males defending temporary spawning territories. We describe a variant social structure where fish occupy permanent home ranges, spawn within or near these home ranges, and are not territorial. Movements of identified terminal-phase and intermediate males and females were mapped in the backreef areas of three coral reefs in Puerto Rico. Locations of spawns were then compared with these home-range maps. All fish used most or all of their morning home range during the afternoon spawning period. Both terminal-phase males and females spawned within or near their home ranges. Males were relatively tolerant of other males during the afternoon spawning period: only one in five encounters between large males resulted in aggressive chases. The location of chases bore no relation to spawning sites, areas of morning foraging, or to home-range borders. A Monte Carlo computer simulation was used to measure home-range dispersion of terminal-phase and intermediate males at our main site. If males were territorial, we should expect their home ranges to be significantly overdispersed within the cumulative area they occupied. During the first year male home ranges were overdispersed but during the second year they were randomly dispersed, even though the same number of terminal-phase males occupied the same study site both years. Differences in social behavior between backreef areas and other areas reported in the literature, and found in other portions of our reefs, may be related to differences in feeding ecology between populations and between different portions of the same reef.     

Contest dynamics for food and reproductive resources are defined by health condition in a dung beetle

Male dung beetles compete to obtain food and females, and early resource recognition and appropriation increase the probability of mating. The outcome of such encounters is expected to be defined by self‐ and the opponent’s health condition. In this study, we analyzed the effect of body condition and immune defense on the contest dynamics between males that rolled a food ball with a partner female (owner males) and intruder males of dung beetle Canthon cyanellus. Body condition was measured as body size, body dry mass, lipid mass, and muscle mass; immune defense was estimated via phenoloxidase activity. Owner males with higher lipid mass contacted the food ball significantly earlier than owner males with lower lipid mass. Individuals with lower phenoloxidase activity started to roll food balls earlier than individuals with higher phenoloxidase activity. Owner males that had higher body dry mass, compared to female partners, began to roll the food ball significantly earlier than male–female pairs with lower differences in dry mass. Heavier males won significantly more contests than lighter males. Our results suggest that the health condition is a key factor related to the dynamics and outcome of male–male contests for resources and females in C. cyanellus. Consequently, differences in individual condition are main determinants of contest outcomes in dung beetles.     

Parental care of the Common Tern Sterna hirundo

Parental care activities of male and female Common Terns Sterna hirundo were recorded over two breeding seasons. Males and females exhibited distinct parental roles throughout a breeding bout. Courtship feeding by males was extensive prior to and during egg-laying, but declined with the onset of incubation. Females performed significantly more incubation behaviour than males although both sexes spent equal time attending at the nest site. During the chick stage, females spent significantly more time on the territory than did males. Chick feeding was largely the responsibility of the male; males fed chicks at a rate approximately three times higher than that of females. In addition, whereas females showed no trend in the size of fish delivered to chicks relative to chick age, the size of fish delivered by males increased with chick age. Courtship feeding activities and extensive chick feeding contributions by male Common Terns appear to outweigh parental contributions by females, contrary to predictions for a monogamous species.     

Energetic requirements of green sturgeon (<Emphasis Type="Italic">Acipenser medirostris</Emphasis>) feeding on burrowing shrimp (<Emphasis Type="Italic">Neotrypaea californiensis</Emphasis>) in estuaries: importance of temperature,reproductive investment,and residence time

Habitat use can be complex, as tradeoffs among physiology, resource abundance, and predator avoidance affect the suitability of different environments for different species. Green sturgeon (Acipenser medirostris), an imperiled species along the west coast of North America, undertake extensive coastal migrations and occupy estuaries during the summer and early fall. Warm water and abundant prey in estuaries may afford a growth opportunity. We applied a bioenergetics model to investigate how variation in estuarine temperature, spawning frequency, and duration of estuarine residence affect consumption and growth potential for individual green sturgeon. We assumed that green sturgeon achieve observed annual growth by feeding solely in conditions represented by Willapa Bay, Washington, an estuary annually frequented by green sturgeon and containing extensive tidal flats that harbor a major prey source (burrowing shrimp, Neotrypaea californiensis). Modeled consumption rates increased little with reproductive investment (<0.4%), but responded strongly (10–50%) to water temperature and duration of residence, as higher temperatures and longer residence required greater consumption to achieve equivalent growth. Accordingly, although green sturgeon occupy Willapa Bay from May through September, acoustically-tagged individuals are observed over much shorter durations (34 d + 41 d SD, N = 89). Simulations of <34 d estuarine residence required unrealistically high consumption rates to achieve observed growth, whereas longer durations required sustained feeding, and therefore higher total intake, to compensate for prolonged exposure to warm temperatures. Model results provide a range of per capita consumption rates by green sturgeon feeding in estuaries to inform management decisions regarding resource and habitat protection for this protected species.     

Ownership,size and reproductive status affect the outcome of food ball contests in a dung roller beetle: when do enemies share?

Theory predicts that asymmetry between contenders influences their ability to defend resources. More recently, some theoretical approaches have also examined the circumstances that might promote sharing of the disputed resources. We tested these hypotheses in males of the ball roller beetle Canthon cyanellus cyanellus. Males fight for possession of a food ball, which is a vital resource used for nesting. We evaluated the role of food resource ownership, body size and reproductive status on the outcome of contests (win, lose or share) between males that rolled a food ball (owners or finders) either alone or with a female partner, when faced with male intruders (or joiners). Large owners of a food ball had a higher probability of victory than small intruders, and small owners had a high probability of losing when faced with large intruders. The reproductive status of both contenders also influenced their chances of winning: previously mated owners of a food ball had a higher probability of winning than virgin owners. Males of a similar size tended to split the food ball, thereby sharing the resource. Our results suggest that competitors may adjust the intensity of their aggression depending at least on their own resource holding power (RHP), the value of the resource in dispute and perhaps even the RHP of their opponents. Sharing the food ball emerges as a fresh solution between similarly matched contestants.