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

Experimental Crosses Between Two Dung Beetle Lineages Show Transgressive Segregation in Physiological Traits

Physiological traits in insects are intrinsically related to their behavior, fitness, and survival and can reflect adaptations to ecological stressors in different environments, leading to population differentiation that may cause hybrid failure. In this study, we characterized five physiological traits related to body condition (body size, body mass, amount of fat, total hemolymph protein, and phenoloxidase activity) in two geographically separated and recently differentiated lineages of Canthon cyanellus LeConte, 1859 within their natural distribution in Mexico. We also performed experimental hybrid crosses between these lineages to better understand the differentiation process and explore the presence of transgressive segregation over physiological traits in them. We found differences between lineages in all traits except body mass, suggesting selective pressures related to different ecological pressures. These differences were also apparent in the transgressive segregation of all traits in F1 and F2 hybrids, except for phenoloxidase activity. Protein content was sexually dimorphic in both parental lineages but was reversed in hybrids, suggesting a genetic basis for the differences between sexes. The negative sign of transgressive segregation for most traits indicates that hybrids would be smaller, thinner, and generally unfit. Our results suggest that these two lineages may undergo postzygotic reproductive isolation, confirming the cryptic diversity of this species complex.

The reproductive behavior of Neotropical dung beetles

Dung beetles display complex reproductive behaviors involving sexual findings, sexual recognition, fighting for mates and food used for nesting, sperm competition, and parental care. Over the past 40 years, significant advances have been made regarding the knowledge of various aspects of the sexual and nesting behavior of Neotropical dung beetles. However, human activities modify the natural habitats of dung beetles at an alarming rate, affecting food availability and altering the ecological functions performed by the species in their different habitats. A deeper understanding of the reproductive behavior of dung beetles may contribute significantly in understanding the evolutionary diversification of these insects and their response to environmental changes. The present study reviews and analyzes studies regarding the sexual and reproductive behavior of Neotropical dung beetle species under field and laboratory conditions. We gathered 132 studies and 146 species; 42% of the available data were based on field observations, 23% on laboratory observations, 30% under both field and laboratory conditions, and 5% unspecified. Our review detected significant knowledge, geographic, and habitat gaps regarding the reproductive behavior of Neotropical dung beetles. Based on our findings, we propose future research goals and alternative methods to measure the behavioral responses of Neotropical dung beetles to the impacts of human activities.

Evolutionary history and diversity in the ball roller beetle Canthon cyanellus

To understand the evolutionary history of species, it is necessary to know the mechanisms for reproductive isolation, divergence-time between populations, and the relative action of the evolutionary forces (e.g., mutation, genetic drift, gene flow) within and between populations of the same, or closely related species. Although Canthon is one of the more diverse genera of neotropical beetles, insufficient research has been done to comprehend the divergent patterns that explain its speciation process. The absence of diagnostic morphological characters and the wide geographic variation of qualitative traits in Scarabaeinae obscures species delimitation, genealogical limits between populations, and its taxonomy. Canthon cyanellus is one of the best-known species in ecological and evolutionary aspects. It is a widely distributed species in the tropical forests of America. Also, the current deforestation has facilitated its incursion into open areas. Individuals from different populations have similar morphological characters but show wide variation in body color throughout their distribution, which makes it difficult to delimit the subspecies that comprise it. Recently, studies have been carried out to elucidate the pre-and postzygotic isolation mechanisms between populations and the historical biogeographical processes favoring cladogenesis events during the Pleistocene. Morphological variation of the male genitalia does not correspond to the phylogeographic structure. However, the morphological differences in one of the pieces of the endophallic sclerites have allowed a preliminary delimitation of some genetically differentiated clades. Finally, we consider that the joint analysis of traditional morphological taxonomy and phylogeography is important to understand the speciation process in the C. cyanellus complex.

Further Insights into Invasion: Field Observations of Behavioural Interactions between an Invasive and Critically Endangered Freshwater Crayfish Using Baited Remote Underwater Video (BRUV)

Competitive behavioural interactions between invasive and native freshwater crayfish are recognised as a key underlying mechanism behind the displacement of natives by invaders. However, in situ investigations into behavioural interactions between invasive and native crayfish are scarce. In Australian freshwater systems, the invasive Cherax destructor has spread into the ranges of many native Euastacus species, including the critically endangered Euastacus dharawalus. Staged contests between the two species in a laboratory setting found E. dharawalus to be the dominant competitor, however, this has yet to be corroborated in situ. Here, we used baited remote underwater video (BRUV) to examine in situ intra- and inter-specific behavioural interactions between E. dharawalus and C. destructor. We sought to evaluate patterns of dominance and differential contest dynamics between the species to provide indications of competition between the two species. We found E. dharawalus to be dominant over C. destructor based on pooled interspecific interaction data and size-grouped interactions where C. destructor was the smaller opponent. Alarmingly, however, when C. destructor was within a 10% size difference the dominance of E. dharawalus was lost, contrasting with the outcomes of the laboratory-staged study. In addition, we report that small C. destructor initiated significantly more contests than larger conspecifics and larger E. dharawalus, a pattern that was not observed in smaller E. dharawalus. Further, intraspecific interactions between C. destructor were significantly longer in duration than intraspecific interactions between E. dharawalus, indicating a willingness to continue fighting. Concerningly, these outcomes point towards inherent and greater aggressiveness in C. destructor relative to E. dharawalus and that only larger E. dharawalus hold a competitive advantage over C. destructor. Therefore, we conclude that C. destructor represents a substantial threat to E. dharawalus through competitive behavioural interactions. Further, due to the disparity between our findings and those produced from laboratory-staged contests, we recommend the use of in situ studies when determining the behavioural impacts of invasive crayfish on natives.

Fighting ability, personality and melanin signalling in free-living Eurasian tree sparrows (Passer montanus)

Background

Individuals' access to resources is often decided during dyadic contests the outcome of which is determined by the fighting (or competitive) ability of the participants. Individuals' fighting ability (termed also as resource-holding power or potential, RHP) is usually associated with individual features (e.g., sex, age, body size) and is also frequently signalled through various ornaments like the black throat patch (bib) in many birds. Individual personality is a behavioural attribute often linked to fighting ability as well. Based on earlier studies, however, the relationship between personality and fighting ability is far from being straightforward. While accounting for sex and body size, we studied whether exploratory behaviour, an aspect of personality, predicts fighting ability when competing for food during winter in free-living Eurasian tree sparrows (Passer montanus). We also investigated whether the bib can serve as a potential indicator of individual competitiveness in this species.

Methods

We captured adult tree sparrows, marked them with a unique combination of colour rings, and collected data about the individuals' sex, body size, bib size and exploratory behaviour. Birds were then released and the agonistic behaviour of the marked individuals was recorded while foraging in groups on bird feeding platforms.

Results

The probability of winning a fight, a proxy for fighting ability of individuals, was not related to exploratory behaviour, in either of the sexes. However, bib size was positively related to probability of winning in females, but not in males. Body size was not associated with probability of winning neither in males, nor in females.

Conclusions

Our results suggest that, at least in tree sparrows, the outcome of dyadic encounters over food during the non-breeding period are not determined by the exploratory personality of individuals. However, our findings provide further support for a status signalling role of the black bib in tree sparrows, and hint for the first time that bib size might function as a status signal in females as well. Finally, our results do not confirm that body size could serve as an indicator of fighting ability (i.e., RHP) in this species.

Fighting over defense chemicals disrupts mating behavior

Studies on intraspecific contest behavior predominantly focus on contests between individuals of the same sex, however contest behavior is also expected to occur between individuals of the opposite sex including possible mates. Here we investigate potential trade-offs between mating and fighting behavior in the turnip sawfly (Athalia rosae). Adults of this species collect chemical defense compounds (clerodanoids) directly from plants but also indirectly by nibbling on conspecifics that have already obtained clerodanoids, a highly aggressive behavioral interaction. An A. rosae individual without clerodanoids may therefore be the potential mate or attacker of an individual of the opposite sex that has gained clerodanoids. To test the effect of clerodanoids on agonistic and mating behavior we paired females and males with or without clerodanoid access in a two-way factorial design. We show that asymmetrical clerodanoid acquisition between female-male pairs causes an increase in agonistic nibbling behavior, irrespective of sex, and moreover that conflict between individuals delays mating behavior. Our study highlights the importance of investigating agonistic intersex interactions, which can occur when adults are able to acquire valuable non-reproductive resources from a potential partner.

Next-generation sequencing, isolation and characterization of 14 microsatellite loci of Canthon cyanellus (Coleoptera: Scarabaeidae)

BACKGROUND

We used Illumina paired-end sequencing to isolate and characterize microsatellites of Canthon cyanellus, a Neotropical roller dung beetle, encompassing several lineages within its distribution range.

METHODS AND RESULTS

We examined C. cyanellus specimens collected at eight different localities in Mexico (two or three specimens per locality). We initially performed amplification tests with 16 loci, but two of which were unsuccessful. The 14 remaining microsatellites were polymorphic, with 2-16 alleles each. The expected and observed heterozygosity ranged from 0.11 to 0.76 and from 0.20 to 0.78, respectively.

CONCLUSIONS

These microsatellites will help to assess structure at the population and lineage levels, identify zones of potential hybridization between lineages, and draw a more precise geographic delimitation of C. cyanellus lineages.

The role of skill in animal contests: a neglected component of fighting ability

What attributes make some individuals more likely to win a fight than others? A range of morphological and physiological traits have been studied intensely but far less focus has been placed on the actual agonistic behaviours used. Current studies of agonistic behaviour focus on contest duration and the vigour of fighting. It also seems obvious that individuals that fight more skilfully should have a greater chance of winning a fight. Here, we discuss the meaning of skill in animal fights. As the activities of each opponent can be disrupted by the behaviour of their rival, we differentiate among ability, technique and skill itself. In addition to efficient, accurate and sometimes precise movement, skilful fighting also requires rapid decision-making, so that appropriate tactics and strategies are selected. We consider how these different components of skill could be acquired, through genes, experiences of play-fighting and of real fights. Skilful fighting can enhance resource holding potential (RHP) by allowing for sustained vigour, by inflicting greater costs on opponents and by minimizing the chance of damage. Therefore, we argue that skill is a neglected but important component of RHP that could be readily studied to provide new insights into the evolution of agonistic behaviour.

Contests over reproductive resources in female roller beetles: Outcome predictors and sharing as an option

Fights among females are frequent, although less attention has been placed on them than on male fights. They arise when females compete for food, oviposition, mates, brooding sites, or access to resources which increase offspring survival. It has been shown that the outcome of female fights may be less predictable by asymmetries in resource holding power, than in male fights. Male roller beetles fight over food resources, food balls, needed for mating and nesting, and it has been show in some species that asymmetries in reproductive experience and resource holding power in terms of size predict fight outcome, including ties in which contenders cut and split the food ball. In this study, we tested the influence of asymmetries in reproductive status (experience) and body size on female fight outcome in the carrion roller beetle Canthon cyanellus cyanellus. As predicted, and as previously found for males of the same species, female reproductive status of both contenders and relative size predict fight outcome. Larger and reproductively experienced contenders have a higher probability of winning. Furthermore, ties are more likely in fights involving opposing asymmetries (vgr. Large reproductively naïve owner versus small reproductively experienced intruder). Also as predicted, food ball splitting is more likely to be started by the predicted loser. This mode of resource sharing may be the result of a fighting strategy in which the costs of continuing to fight are greater than the benefits of not splitting, if a fraction of the disputed resource is more than the minimum needed for the present reproductive needs, and reduces costs associated to a longer fight.

Decline of Ecological Functions Performed by Dung Beetles in Areas of Atlantic Forest and Contribution of Rollers and Tunnellers in Organic Matter Removal

The feeding behavior of the Scarabaeinae subfamily has positive implications on ecosystem functioning. We characterize the necrophagous and coprophagous dung beetle assemblages, and we quantify the removal of swine carrion and domestic dog dung in two areas with different degrees of environmental disturbance in an Atlantic Forest remnant located in Florianopolis, SC, Brazil. The experiment was setup at eight sampling points in each area, by installing one control and two collection and removal assessment arenas for collecting necrophagous dung beetles while simultaneously evaluating the removal of carrion (50 g of rotting pork for 48 h). We used the same sample design with 50 g of domestic dog dung for evaluating the coprophagous dung beetle assemblage and dung removal. Our results indicated that necrophagous dung beetles were more sensitive to environmental disturbance owing to a lower richness and changes in species dominance, which resulted in a lower removal in the areas with greater disturbance and lower environmental quality (39.6% carrion removal) in relation to less disturbed areas (75.1% carrion removal). The dung beetle assemblages were similar in structure and removal rates between areas (80% of dung was removed). In assessing the influence of richness, abundance, and biomass of dung beetles on resource removal both for the whole assemblage and for each separate functional guild, only the abundance and biomass of rollers contributed significantly to dung removal. These results highlight the implications of environmental disturbances on the functions of dung beetles, which respond differently according to the resource they use.

Effects of age and experience on contest behavior in the burying beetle, Nicrophorus vespilloides

Aggression and likelihood of winning contests are expected to change as a male ages. We test this idea in burying beetles, a species which competes over small mammal carcasses as a breeding resource. We find that male size relative to his opponent is far more important in determining contest outcome than any effects of age or social experience.

Contest behavior forms an important part of reproductive investment. Life-history theory predicts that as individuals age and their residual reproductive value decreases, they should increase investment in contest behavior. However, other factors such as social experience may also be important in determining age-related variation in contest behavior. To understand how selection acts on contest behavior over an individual’s lifetime, it is therefore important to tease apart the effects of age per se from other factors that may vary with age. Here, we independently manipulate male age and social experience to examine their effects on male contest behavior in the burying beetle Nicrophorus vespilloides. We found that social experience, but not age, influenced male contest behavior but that these changes in behavior did not alter contest outcomes. Male size (relative to his opponent) was overwhelmingly the most important factor determining contest outcome. Our results suggest that in systems with high variation in fighting ability among males, there may be little opportunity for selection to act on factors that influence contest outcomes by altering motivation to win.