Trilobite tridents demonstrate sexual combat at 400 Mya

The Devonian trilobite Walliserops carries a remarkable anterior cephalic trident posing a challenge to functional interpretation. A unique teratological specimen of Walliserops trifurcatus showing four, rather than three tines, is inconsistent with possible hypotheses connecting the trident to feeding techniques and suggests a sexually selected function. Malformations in a variety of living organisms support this conclusion. Morphometric comparisons to similar structures used for intraspecific combat in dynastine beetles show that the trident occupies a comparable shape space consistent with the hypothesis that it was a sexual combat weapon, the oldest reported example of its kind. This lends further credibility to the idea that some trilobites may have been strongly sexually dimorphic.

Phylogeography Approach of Diloboderus abderus (Coleoptera: Melolonthidae) in the Southern Cone of America

Diloboderus abderus (Sturm, 1826) (Coleoptera: Melolonthidae) is a serious soil pest of corn, wheat, oat, and natural and cultivated pastures in Argentina, Paraguay, Uruguay, and southern Brazil. Despite its economic importance, the genetic diversity and population structure of D. abderus remain unknown. We sequenced a fragment of the mitochondrial gene cytochrome oxidase I region (COI), of six populations of D. abderus from the Southern Cone of America. The mtDNA marker revealed a high haplotype diversity, high pairwise F_ST values, and significant genetic variations among populations. No correlation was found between genetic and geographical distances, yet the most common haplotype (Dab01) was present in four out of the six populations. Analysis of molecular variance showed that most of the variation was within populations of D. abderus. Tajima's D and Fu's F_S tests indicated no evidence that D. abderus populations are under recent expansion. Our results indicate that genetic-based traits will likely remain localized or spread slowly, and management strategies need to be undertaken on a small scale.

Contribution to the Species of Oxyligyrus Arrow (Coleoptera, Melolonthidae) of the Peruanus Species Group with the Description of Two New Species

Two new species of the genus Oxyligyrus Arrow, 1908 from the peruanus species group are described from Brazil and compared with other species of the genus Oxyligyrus limeirai sp. nov., from Maranhão state and Oxyligyrus vazdemelloi sp. nov. from Mato Grosso state. A key to the peruanus complex and a distribution map of their known brazilian localities is also provided. New state records from Brazil are also presented for Oxyligyrus zoilus (Olivier 1789) the most widespread species of the genus and for O. acutus Endrödi, 1966.

Endothermy in the temperate scarab Cyclocephala signaticollis

The increase in body temperature over that of the environment has been frequently reported in insects, in particular in relation with flight activity. Scarab beetles of the genus Cyclocephala living in tropical areas are known to exploit the heat produced by thermogenic plants, also producing heat by endothermy. Here, we report the first case of endothermy in a species of this genus living in a temperate region, Cyclocephala signaticollis. We characterised the phenomenon in this beetle using infrared thermography and exposing them to different thermal conditions. We evaluated the frequency of endothermic bouts, the nature of their periodic occurrence and their association with the activity cycles of the beetles. We found that endothermy occurs in both males and females in a cyclic fashion, at the beginning of the night, around 21:00 local time. The mean temperature increase was of 9 °C, and the mean duration of the bouts was 7 min. During endothermic bouts, the temperature of the thorax was on average 3.6 °C higher than that of the head and 4.8 °C above that of the abdomen. We found no differences between females and males in the maximum temperature attained and in the duration of the endothermy bouts. The activity period of the beetles extends throughout the whole night, with maximum activity between 22:00 and 23:00. By subjecting the beetles to different light regimes we were able to determine that the rhythm of endothermy is not controlled by the circadian system. Finally, we experimentally tested if by performing endothermy the scarabs try to reach a particular body temperature or if they invest a given amount of energy in heating up, instead. Our results indicate that at lower ambient temperature beetles show higher increase in body temperature, and that endothermy bouts last longer than at relatively higher ambient temperatures. We discuss our findings in relation to the ecology and behaviour of this beetle pest.

2-Alkyl-3-methoxypyrazines are potent attractants of florivorous scarabs (Melolonthidae, Cyclocephalini) associated with economically exploitable Neotropical palms (Arecaceae)

BACKGROUND

2-Alkyl-3-methoxypyrazines (MPs) are naturally occurring aromatic compounds involved in insect chemical communication as both pheromones and allelochemicals. Although rarely characterized in floral scents, they have been identified as major constituents in headspace samples from palm inflorescences and evidence pointed towards their function as attractive cues for scent-oriented pollinators, as well as florivores. In this study, we investigated the occurrence of MPs in economically exploitable palms belonging to Acrocomia and Attalea through headspace floral scent analysis and assessed their role in the selective attraction of flower-feeding cyclocephaline scarabs (Melolonthidae, Cyclocephalini) in field bioassays conducted in Brazil and Colombia.

RESULTS

Three different MPs were identified among floral headspace samples of Acrocomia aculeata, Acr. intumescens, Attalea butyracea and Att. insignis: 2-isopropyl-3-methoxypyrazine (IPMP), 2-isobutyl-3-methoxypyrazine (IBMP) and 2-(sec-butyl)-3-methoxypyrazine (SBMP). Their combined estimated total scent emissions per inflorescence ranged from 246 μg h-1 to 6.2 mg h-1 . Scented traps, individually baited with either IPMP or SBMP, resulted in species-selective and high yield captures of Cyclocephala amazona and C. distincta, known florivores associated with over 20 different species of Neotropical palms.

CONCLUSIONS

The identification of MPs as potent kairomones could prove instrumental in integrated pest management plans for these insects in emerging oil-yielding crops in South America, including those of the wine palm (Att. butyracea) and macaw palms (Acrocomia spp.). © 2018 Society of Chemical Industry.

Structural adaptations to diverse fighting styles in sexually selected weapons

The shapes of sexually selected weapons differ widely among species, but the drivers of this diversity remain poorly understood. Existing explanations suggest weapon shapes reflect structural adaptations to different fighting styles, yet explicit tests of this hypothesis are lacking. We constructed finite element models of the horns of different rhinoceros beetle species to test whether functional specializations for increased performance under species-specific fighting styles could have contributed to the diversification of weapon form. We find that horns are both stronger and stiffer in response to species-typical fighting loads and that they perform more poorly under atypical fighting loads, which suggests weapons are structurally adapted to meet the functional demands of fighting. Our research establishes a critical link between weapon form and function, revealing one way male-male competition can drive the diversification of animal weapons.