Exaggerated horns are a characteristic feature of many male rhinoceros beetles. We surveyed and compared the scaling relationships of these sexually-selected weapons for 31 Dynastinae species with different degrees of horn exaggeration. We found that nearly all rhinoceros beetle species were male dimorphic, that the allometric slope of major males was consistently shallower than the slope of minor males, and that the decrease in slope was greatest among species with the most exaggerated horns. These patterns are consistent with the curved allometries of stag beetle mandibles and giraffe weevil rostra, and suggest that the depletion of developmental resources is a general phenomenon limiting the continued exaggeration of insect weapons. The dimorphisms in horn morphology are expected to correspond to behavioral differences between major and minor males, but little is still known about the mating tactics of most rhinoceros beetle species. Future studies on the relative benefits and performance of horns during male-male combat are needed to fully understand the diversity of horn allometries and the evolution of exaggerated structures.

We have yet to adequately quantify the impacts of invaders in their non-native ranges relative to their native ranges. Such biogeographical comparisons are crucial to better understand the role of invasive species in plant-plant interactions and in the evolution of community organization. Using Solidago canadensis, we conducted field surveys in the native range (North America) and non-native range (Europe) and correlated stem density and aboveground biomass of Solidago with associated plant species richness and diversity indices. We also conducted experiments to compare the competitive and allelopathic impact of Solidago on the growth of species from its native and non-native ranges. In the field, increasing stem density and biomass of Solidago correlated with more significant decreases in total species richness and two diversity indices in Europe than in North America. Solidago strongly suppressed both European species and North American species in competition experiments, but this competitive effect did not differ between species from the different ranges. However, root extracts from Solidago strongly suppressed the root growth of European species as a group, but not North American species as a group. Our results indicate that the biogeographic origin of species can have important effects on plant interactions and community organization.

Ticks are widespread parasites of vertebrates and major vectors of pathogens to humans, domestic animals, and wildlife. In southern Africa, numerous tick species transmit diseases of economic and health importance. This study aimed to describe the occurrence of ticks and tick-borne pathogens in multiple land-use types and the possible role of ticks in the transmission of pathogen species. Using molecular techniques, we screened 1716 ticks for infection by rickettsial bacteria and protozoans. To characterize pathogen identity, we sequenced multiple loci from positive samples and analyzed sequences within a phylogenetic framework. Across the seven tick species collected as nymphs or adults, we detected Rickettsia, Anaplasma, Ehrlichia, Babesia, Hepatozoon, and Theileira species. We found that some tick species and tick-borne pathogens differed according to land use. For example, we found a higher density of Haemaphysalis elliptica and higher prevalence of Rickettsia in H. elliptica collected from savanna grasses used for livestock grazing near human settlements than savanna grasses in conservation areas. These findings highlight the importance of comprehensive surveillance to achieve a full understanding of the diversity and ecology of the tick-borne pathogens that can infect humans, domestic animals, and wildlife.

Land use influences the prevalence and distribution of ticks due to the intimate relationship of ticks with their environment. This relationship occurs because land use alters two essential tick requirements: vertebrate hosts for blood meals and a suitable microclimate when off-host. Given the risks to human and animal health associated with pathogens transmitted by ticks, there is an ongoing need to understand the impact of environmental drivers on tick distributions. Here, we assessed how landscape features, neighborhood effects, and edges influenced tick occupancy and abundance across an agricultural landscape in southern Africa. We found that Rhipicephalus appendiculatus and Rhipicephalus simus increased in abundance closer to protected savanna, while Haemaphysalis elliptica increased in abundance closer to human habitation. The composition of the landscape surrounding savanna patches also differentially influenced the occupancy of each tick species; H. elliptica was more likely to be found in savanna patches surrounded by subsistence agriculture while R. appendiculatus and R. simus were more likely to be found in savanna surrounded by sugarcane monocultures. At the local scale we found that R. appendiculatus and R. simus avoided savanna edges. The availability of hosts and variation in vegetation structure between commercial agriculture, subsistence agriculture, and savanna likely drove the distribution of ticks at the landscape scale. Understanding how anthropogenic land use influences where ticks occur is useful for land use planning and for assessing public and animal health risks associated with ticks and tick-borne diseases.

Sexual selection has equipped male rhinoceros beetles with large horns on their head and prothorax to aid in battle over access to females. Horns are used to pry and dislodge opponents from resource sites that attract females, so an optimal horn should be able both to withstand the high stresses imposed during fights, and to resist deflection in response to these loads. We examined the cross‐sectional morphology of horns using micro‐computed tomography scanning to determine how horn structure changes with horn length to withstand the different fighting loads. Specifically, we measured the second moment of area of horns within and among rhinoceros beetle species to assess whether changes in cross‐sectional morphology accompany changes in body size in order to maintain high strength and stiffness during fights. We find that the second moment of area of horns increases with body size both intra‐specifically and inter‐specifically, and that these relationships closely fit those predicted if horns have been selected to be strong and stiff fighting structures. Our results therefore support the hypothesis that rhinoceros beetle horns are structurally adapted for combat.