Visual Signals of Individual Quality in a European Solitary Founding Paper Wasp

Conventional signals are maintained via social costs and commonly used in the animal kingdom to assess conspecifics' agonistic ability during disputes over resources. In the last decade, some experimental studies reported the existence of visual conventional signals in several social wasp species, being good rank predictors in different social contexts. Females of the social wasp Polistes gallicus do not cooperate to start nests but they often try to usurp conspecific nests. Here, we showed that the reproductive females of this species have variable facial colour patterns that function as conventional signals. Wasps with larger black spots on their clypeus are more likely to successfully overwinter, are larger, and are better at fighting and at holding a nest. Furthermore, in field experiments, resident foundresses rely on facial pattern to assess usurpers' fighting abilities, modulating their defence reaction accordingly, so that rivals with larger black spot receive more aggression than rivals with smaller or no black spots on the clypeus. Our study reveals that visual recognition abilities are widespread among paper wasps that, regardless of their social biology, face similar selective pressures within competitive contexts.     

An intimidating ornament in a female pipefish

A sexually selected signal may serve a dual function being bothattractive to mates and deterring rivals. Presently, there arefew unambiguous demonstrations of an ornament functioning inboth a mate choice and mate competition context and none regardingfemale ornaments. We have shown earlier that a temporary ornament,a striped pattern, in a sex-role reversed female pipefish, Syngnathustyphle, attracts males. Here we show that this ornament alsointimidates rival females: in one experiment a male could interactwith either 1 or 2 females. Latency until copulation was longerwhen 2, rather than 1, females were present. Moreover, when2 females were present, competition lasted longer and time untilmating took place increased when females displayed their ornamentsmore equally. In another experiment, a focal female could see1 stimulus female and 1 stimulus male, the latter 2 being unawareof each other. The ornament of the stimulus female was manipulated,either strengthened by being painted black or left unalteredby being sham-painted. As a result, focal females experiencingblack-painted stimulus females decreased courtship as well ascompetitive activities compared with focal females seeing sham-paintedfemales. Moreover, focal females seeing black-painted femalesdisplayed less of their own ornament compared with controls.This decrease was due to a decrease in display toward malesrather than to stimulus females. Thus, this female ornamentindeed has a dual function, attracting mates and deterring rivals.In addition, the social costs invoked by this intimidating effecton rivals may help to maintain signal honesty.     

Intra-sexual Dimorphism in Male Mandibles and Male Aggressive Behavior in the Broad-Horned Flour Beetle Gnatocerus cornutus (Coleoptera: Tenebrionidae)

In the stored-product beetle, the broad-horned flour beetle, Gnatocerus cornutus (Fabricius), all males possess enlarged mandibles, widened gena, and a pair of small horns on the vertex, but females lack these completely. Observations of male-male interactions of G. cornutus showed that larger individuals won male-male fights, and that the mandibles were used as weapons. Morphological analysis based on the non-linearity test of Eberhard and Gutierrez's model (1991) showed that intra-sexual dimorphism in males was only found in the mandibles used in male-male combat, but not in the gena and horns. This beetle can be an ideal model for evolutionary studies of exaggerated weapons for male combat, because rearing successive generations and observing male fighting are easy.     

Ladder Use and Clubbing by a Bonobo (Pan paniscus) in Apenheul Primate Park

Two types of tool use were shown by a captive bonobo (Pan paniscus) in a large outdoor enclosure at Apenheul Primate Park in The Netherlands. A wild‐born young adult female (estimated to be 9 years old) used fallen branches as ladders to bypass protective sheaths to gain access to trees. Later she used a branch as a weapon to beat to death a peahen (Pavo cristatus). None of the other bonobos in the group were seen to use branches as either ladders or weapons. Zoo Biol 21:607–611, 2002. © 2002 Wiley‐Liss, Inc.     

Adaptations to humeral torsion in medieval Britain

Adaptations to the humeral torsion angle have been identified in the professional throwing athlete. This movement pattern increases the humeral torsion angle, and also increases the extent of external rotation movements in the dominant, throwing limb when compared with the nondominant limb. The purpose of this paper is to test the hypothesis that the humeral torsion angle is an adaptation to upper limb use. This project examines the humeral torsion angle in a number of medieval British populations, as well as a modern cadaver-based sample. The results identify significant differences in the humeral torsion angle both between and within male (P < 0.001, ANOVA) and female (P < 0.014, ANOVA) populations, although the results are not consistent with expected behavior patterns. Statistically significant differences between males and females within the same site were identified in 2 of the 5 samples examined. The mean level of bilateral asymmetry does not approach that reported for the professional throwing athlete. However, a number of individuals have high levels of asymmetry in excess of that identified in the professional throwing athlete. This analysis demonstrates the need for individual rather than population-based analyses, as the heterogeneity within population samples obscures individual variation in activity patterns. The diversity within British medieval society and a lack of specific known behaviors prevent further identification of the functional significance of the humeral torsion angle within the archaeological record examined here.     

Armaments and ornaments: an evolutionary explanation of traits of dual Utility

Secondary sexual characters in many species function both in male-male competition and as cues for female choice. Based on a literature compilation of existing knowledge of traits with this dual function, we propose that they commonly arise through intersexual selection processes and serve as honest signals to other males regarding fighting ability or dominance. Faking these traits, here called armaments, (i.e. weapons and status badges) is difficult, as they are constantly put to trial in male-male contests. Females that subsequently utilize them as indicators of male phenotypic quality when selecting a partner will benefit by acquiring males of higher quality to father their offspring. Thus, evolution of armaments through male-male competition is seen as a usually initiating process, whereas female choice later may assume a role as an additional selective factor. The reverse, that males use information from traits evolved through female choice, is, however, also possible. The traditional view of independently evolved and temporarily unordered intra- and intersexual selection processes fails to explain dual trait functions. Moreover, our model may more satisfyingly than traditional ones explain how trait honesty and trait genetic variance are maintained: theoretical and empirical evidence suggests that such honesty and variation are more easily maintained under male-male competition than under female choice.     

Heritability of male mandible length in the stag beetle Cyclommatus metallifer

Numerous coleopteran species express male‐specific “weapon traits” that often show size variations among males, even within a single population. Many empirical studies have demonstrated that environmental conditions during development affect absolute weapon size. However, relatively few studies in horned beetles support the hypothesis that the relationship between weapon size and body size, also referred to as a “scaling relationship” or “static allometry”, is largely determined by genetic factors. In this study, the heritability of absolute mandible length and static allometry between mandible length and body size were estimated in the stag beetle Cyclommatus metallifer. While no significant heritable variation was observed in absolute mandible length, high heritability (h² = 0.57 ± 0.25) was detected in the static allometry between mandible length and body size. This is the first report on the genetic effect on male mandible size in Lucanidae, suggesting that absolute mandible size is largely determined by environmental conditions while the static allometry between weapon size and body size is primarily determined by genetic factors.