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

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.

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.