Fighting scars: heavier gladiator frogs bear more injuries than lighter frogs

Evolution of territoriality in Hylinae treefrogs: Ecological and morphological correlates and lineage diversification

Given the diverse nature of traits involved in territorial defence, they may respond to different selective pressures and then exhibit distinct patterns of evolution. These selective pressures also may cause territorial behaviour to be associated with environmental and morphological variables. Such associations, however, have mostly been studied at the intraspecific level, being phylogenetic analyses of territoriality in a broad taxonomic framework rare in the literature. We used the anuran subfamily Hylinae to test (1) whether two territorial-behaviour traits with different levels of aggression-territorial call and physical combat-are evolutionarily more labile than a morphological trait used in physical combat-the spine-shaped prepollex; (2) whether reproduction in lentic waters and phytotelmata, as well as resource scarcity, might favour the occurrence of territoriality; (3) if physical combat is more important than territorial call for the evolution of body size and sexual size dimorphism and (4) the relationships between territorial-behaviour traits and lineage diversification. We mainly used the literature to build two datasets with different levels of certainty. Territorial-behaviour traits exhibited intermediate levels of phylogenetic signal in Hylinae, whereas the phylogenetic signal for the presence of the spine-shaped prepollex was strong. We found support for the hypothesis that reproduction in lentic water favours the occurrence of territorial behaviour, because the expression of territorial-behaviour traits was more associated with reproduction in lentic than in lotic waters. Territorial-behaviour traits were not correlated with annual precipitation nor with habitat complexity. Body size and sexual size dimorphism were not correlated with the presence of territorial call nor with physical combat. We identified negative correlations between diversification rates and physical combat. Relationships of territorial call and physical combat with diversification rates suggest that these territorial behaviours influence evolutionary processes in different ways.

Biomechanics influence sexual dimorphism in the giant mesquite bug, Thasus neocalifornicus

In many species, males possess specialized weaponry that confers benefits during male-male combat. Because male weapons are often disproportionately larger versions of preexisting body parts, females often possess reduced versions of male weaponry. Most research focuses exclusively on sexual dimorphism in the size of male and female weapons, even though other aspects such as weapon performance can also explain the evolution of weapon sexual dimorphism. In the giant mesquite bug, Thasus neocalifornicus, males wield exaggerated hindlegs that aid in locomotion and are used as weapons to generate forceful squeezes during combat. However, female T. neocalifornicus hindlegs are relatively inconspicuous and only used for locomotion. To understand the intricacies of weapon sexual dimorphism in T. neocalifornicus hindlegs, we measured the allometry of their hindlegs morphology, biomechanics, and performance. Males and females had relatively similar sized legs when concerning only linear measurements: hindleg length did not differ between the sexes (both for intercept and slope), but males do have relatively wider hindlegs (greater intercepts). Regarding performance, however, males were relatively and proportionally stronger than females. Furthermore, the output lever of male hindlegs scales hypoallometrically and the tibial spine maintains its position as the hindlegs grows, both of which maintain the hindlegs' biomechanical efficiency as they increase in size. Overall, our finding demonstrates that selection on the performance and biomechanics of sexually selected weapons can influence the expression of sexual dimorphism, by exaggerating some aspects of the weapons morphology-but constraining others.

Prepollex diversity and evolution in Cophomantini (Anura: Hylidae: Hylinae)

Several species of Cophomantini are known to have an enlarged prepollex, commonly modified as an osseous spine. We surveyed the osteology and myology of the prepollex and associated elements of 94 of the 190 species of Cophomantini, sampling all genera, except Nesorohyla. Two distinct prepollex morphologies were found: a blade-shaped and a spine-shaped morphology. We described the observed variation in 17 discrete characters to study their evolution in the most inclusive phylogenetic hypothesis for Cophomantini. Both morphologies evolved multiple times during the evolutionary history of this clade, but the origin of the spine-shaped distal prepollex in Boana and Bokermannohyla is ambiguous. The articulation of metacarpal II with the prepollex through a medial expansion of the metacarpal proximal epiphysis is a synapomorphy for Boana. The shape of the curve of the spine, and a large post-articular process of the distal prepollex, are synapomorphies for the Boana pulchella group, the latter being homoplastic in the Bokermannohyla martinsi group. Muscle character states associated with the spine-shaped prepollex are plesiomorphic for Cophomantini. We discuss evolution, function, behaviour and sexual dimorphism related to the prepollical elements. A bony spine is associated with fights between males, but forearm hypertrophy could be more related with habitat than with territorial combat.

Communication across multiple sensory modes: quantifying the rich behavioural repertoire of a Neotropical torrent frog

Anuran communication involves different channels of signal transmission, including acoustic, chemical, seismic, tactile, and visual stimuli. If emitted in combination, the components of the different channels form the multimodal communication, which can be important to reinforce, complement, or transfer fundamental information. This is especially key for species that dwell in noisy environments, such as Hylodes phyllodes. This rheophilic frog species has a complex behavioural repertoire, including acoustic and visual signals. In this study, we quantified and characterized the multimodal communication of this species. We identified and characterized advertisement, territorial, and encounter calls. Additionally, we compared the advertisement calls from the same males when emitted with one or both vocal sacs expanded and found that they differed in temporal and spectral parameters. Hylodes phyllodes performed 16 visual displays, which varied among individuals and populations. We elucidate that visual signalling is easily quantifiable and could be used to compare individuals, populations, and species, as typically done with anuran acoustic signals.

Reproductive ecology and territorial behavior of Boana goiana (Anura: Hylidae), a gladiator frog from the Brazilian Cerrado

Anuran males and females adopt different reproductive and behavioral strategies in different contexts. We investigated the reproductive ecology and territorial behavior of the treefrog Boana goiana (B. Lutz, 1968) from the Brazilian Cerrado. We hypothesized that competitor density/proximity would increase the behavioral responses of B. goiana males, and that mating would be assortative. We also tested if the number of eggs correlates with female size and if there is a trade-off between clutch size and egg size. We conducted two territoriality experiments to test the effects of male size, competitor proximity and competitor density. Larger males called more in the presence of a second male. In the second experiment, the largest males emitted more calls and the distance to the nearest male increased as resident males called more. In both experiments, the number of calls was influenced by either male size or spacing between males. Some males behaved as satellites, probably to avoid fights. Our analyses indicate that females choose males with similar sizes to their own, corroborating our hypothesis of size-assortative mating. We found no relationships between female size and clutch size/volume, and between egg size and number of eggs per clutch. We also report multiple spawning for this species. The low incidence of physical combats and the spacing pattern indicate that this species relies almost solely on calls to resolve contests, which could be explained by low motivation, or simply because males avoid combats to decrease injury risks. Thus, acoustic or even multimodal communication seems crucial for social interactions of B. goiana.