Speed and accuracy in nest-mate recognition: a hover wasp prioritizes face recognition over colony odour cues to minimize intrusion by outsiders

Social insects have evolved sophisticated recognition systems enabling them to accept nest-mates but reject alien conspecifics. In the social wasp, Liostenogaster flavolineata (Stenogastrinae), individuals differ in their cuticular hydrocarbon profiles according to colony membership; each female also possesses a unique (visual) facial pattern. This species represents a unique model to understand how vision and olfaction are integrated and the extent to which wasps prioritize one channel over the other to discriminate aliens and nest-mates. Liostenogaster flavolineata females are able to discriminate between alien and nest-mate females using facial patterns or chemical cues in isolation. However, the two sensory modalities are not equally efficient in the discrimination of ‘friend’ from ‘foe’. Visual cues induce an increased number of erroneous attacks on nest-mates (false alarms), but such attacks are quickly aborted and never result in serious injury. Odour cues, presented in isolation, result in an increased number of misses: erroneous acceptances of outsiders. Interestingly, wasps take the relative efficiencies of the two sensory modalities into account when making rapid decisions about colony membership of an individual: chemical profiles are entirely ignored when the visual and chemical stimuli are presented together. Thus, wasps adopt a strategy to ‘err on the safe side’ by memorizing individual faces to recognize colony members, and disregarding odour cues to minimize the risk of intrusion from colony outsiders.     

Which Factors Affect Sex Ratio of Spined Loach (genus Cobitis) in Lake Müggelsee?

The distribution and extent of chemical alarm signaling systems among some families of fishes, including the Cottidae, remains unclear. In laboratory experiments, we tested whether reticulate sculpins, Cottus perplexus, respond to chemical alarm signals released by injured conspecifics. Sculpins decreased movement following exposure to skin extracts from conspecifics, but did not respond to cues of syntopic speckled dace, Rhinichthyes osculus, or allotopic swordtails, Xiphophorous helleri. Additional tests demonstrated that the responses of sculpins to alarm cues were dependent on the hunger level of the test fish. Sculpins deprived of food for 2 days failed to respond to conspecific alarm cues, however, the same individuals fed to satiation did respond to alarm cues.     

Mate recognition systems in a species flock of Mexican pupfish

The pupfishes of Lake Chichancanab (Mexico) provide a unique opportunity to study the evolution of premating reproductive barriers. This group of endemic species is of recent origin and the lineages differ in morphological traits indicating trophic specialization, but show very little genetic change. We studied the function of visual and chemical cues in the mate recognition system of three morphospecies, Cyprinodon beltrani, C. labiosus and C. maya. Only in C. maya, which is genetically the most distinct member of the group, do females show the ability to identify males of their own type, both visually and chemically. C. labiosus females discriminated between their own and C. beltrani males based on chemical but not visual cues. C. beltrani, which is morphologically the least differentiated member of the group, showed no interspecific mate recognition. Females responded more strongly to the visual and chemical cues of their own males than to their own females, but they did not discriminate between their own males and those of the other two morphospecies based upon either type of cue. These results suggest that different levels of behavioural isolation have been established: most isolated is C. maya, and the least is C. beltrani. C. labiosus has an intermediate position. The results also suggest that species recognition cues based on different sensory modalities do not necessarily evolve together, and may evolve at different rates.     

Is love in the air or at first sight? Mate finding cues used by sympatric male velvet ants (Hymenoptera: Mutillidae)

Mate finding has been examined in a wide range of hymenopteran families, with the greatest knowledge from social species and parasitoids used in pest management. Velvet ants (Hymenoptera: Mutillidae) provide a unique system to study mate finding because short‐lived flying males must find solitary, wingless females that have spatially and temporally dispersed emergence. Based on limited field observations, it is thought that male velvet ants may use visual, chemical, and vibratory cues for mate finding, though there have been no controlled experiments to test these hypotheses. Using choice experiments, this study aims to determine the role of visual and airborne chemical cues used in female detection by three sympatric species of Dasymutilla males. We find that visual cues are not used for initial female detection and that airborne chemicals are sufficient for female detection. We also discover that males readily approach females of different species, indicating airborne chemicals are not used for species recognition. Despite the lack of discrimination by males, we determined that the sympatric, morphologically similar species show no genetic introgression, and therefore some other isolating mechanism must be at play after males make initial contact with the females.     

Functions of the testicular gland in two blenniid fishes, Salaria (=Blennius) pavo and Lipophrys (= Blennius) dalmatinus (Blenniidae, Teleostei) as revealed by electron microscopy and enzyme histochemistry

The functions of the testicular gland in two different blenniid fishes, Salaria pavo and Lipophrys dulmutinus , are described by fine structural and enzyme histochemical methods. In the testes of the two fishes no mature spermatozoa are found. Sperrniogenesis occurs only until the spermatidal stage. Spermatids are released into the testicular gland. During the spawning period the testicular gland functions in differentiation of spermatids, nutrition of spermatids, and secretion of sialomucins. After spawning, the testicular gland has phagocytotic functions in resorbtion of remaining spermatids, which are transformed into lipids in the gland cells. During the interspawning period the testicular gland is a storage reservoir for lipids and phospholipids which are re-transformed into testicular gland secretion in the next reproductive season. Testicular gland cells themselves do not have steroidogenetic functions, but steroids are synthesized by interstitial cells homologous to Leydig cells in other fish. Possible explanations for the reduction of the testis in L. dalmatinus and implications of the testicular gland in taking over testicular functions are discussed.     

Assessing the potential information content of multicomponent visual signals: a machine learning approach

Careful investigation of the form of animal signals can offer novel insights into their function. Here, we deconstruct the face patterns of a tribe of primates, the guenons (Cercopithecini), and examine the information that is potentially available in the perceptual dimensions of their multicomponent displays. Using standardized colour-calibrated images of guenon faces, we measure variation in appearance both within and between species. Overall face pattern was quantified using the computer vision ‘eigenface’ technique, and eyebrow and nose-spot focal traits were described using computational image segmentation and shape analysis. Discriminant function analyses established whether these perceptual dimensions could be used to reliably classify species identity, individual identity, age and sex, and, if so, identify the dimensions that carry this information. Across the 12 species studied, we found that both overall face pattern and focal trait differences could be used to categorize species and individuals reliably, whereas correct classification of age category and sex was not possible. This pattern makes sense, as guenons often form mixed-species groups in which familiar conspecifics develop complex differentiated social relationships but where the presence of heterospecifics creates hybridization risk. Our approach should be broadly applicable to the investigation of visual signal function across the animal kingdom.     

Brain aromatase mRNA expression in two populations of the peacock blenny Salaria pavo with divergent mating systems

Aromatase, the key enzyme in the conversion of androgens to estrogens, regulates the availability of these hormones in tissues and controls many physiological and behavioral processes. In fish and other vertebrates, the regulation of aromatase expression in the brain has been implicated in the modulation of male sexual and aggressive behaviors. Here, the pattern of mRNA expression of the brain aromatase isoform (encoded by the CYP19A2 gene also referred as CYP19b) was quantified at the peak of spawning season in brain macroareas from males and females of the blenny Salaria pavo originated from two populations displaying male alternative reproductive tactics but differing in their mating systems. In Trieste (Adriatic) nesting males aggressively defend nests and take the initiative in courtship and perform sexual displays more often than females while in Ria Formosa (Southern Portugal) the pattern is reversed as a result of shortage of appropriate nesting sites. Nesting males from Ria Formosa had overall higher levels of brain aromatase mRNA expression than nesting males from Trieste, suggesting a higher brain estrogen synthesis in these males. Since in some fish species exogenous estradiol administration has been shown to decrease sexual and agonistic behaviors, the higher levels of brain aromatase in Ria Formosa nesting males may explain their reduced expression of sexual and aggressive displays when compared with nesting males from Trieste. Alternatively, the higher brain aromatase levels in nesting males from Ria Formosa could be a mechanism to decrease the putative androgen-induced activation of aggressive and sexual displays by reducing the local availability of androgens through their metabolization into estrogens. Although females and parasitic female-like males also differ in their displays between populations, the interpopulational pattern of brain aromatase mRNA expression was similar, suggesting that other neuroendocrine agents mediate the expression of female and female-like behaviors. In conclusion, brain aromatase availability seems like a probable mechanism to regulate the effects of steroids on the brain circuits underlying the expression of sexual and agonistic displays in S. pavo.     

Learn and live: predator experience and feeding history determines prey behaviour and survival

Determining how prey learn the identity of predators and match their vigilance with current levels of threat is central to understanding the dynamics of predator–prey systems and the determinants of fitness. Our study explores how feeding history influences the relative importance of olfactory and visual sensory modes of learning, and how the experience gained through these sensory modes influences behaviour and survival in the field for a juvenile coral reef damselfish. We collected young fish immediately prior to their settlement to benthic habitats. In the laboratory, these predator-naïve fish were exposed to a high- or low-food ration and then conditioned to recognize the olfactory cues (odours) and/or visual cues from two common benthic predators. Fish were then allowed to settle on reefs in the field, and their behaviour and survival over 70 h were recorded. Feeding history strongly influenced their willingness to take risks in the natural environment. Conditioning in the laboratory with visual, olfactory or both cues from predators led fish in the field to display risk-averse behaviour compared with fish conditioned with sea water alone. Well-fed fish that were conditioned with visual, chemical or a combination of predator cues survived eight times better over the first 48 h on reefs than those with no experience of benthic predator cues. This experiment highlights the importance of a flexible and rapid mechanism of learning the identity of predators for survival of young fish during the critical life-history transition between pelagic and benthic habitats.