Early social context does not influence behavioral variation at adulthood in ants

International audienceEarly experience can prepare offspring to adapt their behaviors to the environment they are likely to encounter later in life. In several species of ants, colonies show ontogenic changes in the brood-to-worker ratio that are known to have an impact on worker morphology. However, little information is available on the influence of fluctuations in the early social context on the expression of behavior in adulthood. Using the ant Lasius niger, we tested whether the brood-to-worker ratio during larval stages influenced the level of behavioral variability at adult stages. We raised batches of 20 or 180 larvae in the presence of 60 workers until adulthood. We then quantified the activity level and wall-following tendency of callow workers on 10 successive trials to test the prediction that larvae reared under a high brood-to-worker ratio should show greater behavioral variations. We found that manipulation of the brood-to-worker ratio influenced the duration of development and the size of individuals at emergence. We detected no influence of early social context on the level of between- or within-individual variation measured for individual activity level or on wall-following behavior. Our study suggests that behavioral traits may be more canalized than morphological traits

The inheritance of female colour polymorphism in Ischnura genei (Zygoptera: Coenagrionidae), with observations on melanism under laboratory conditions

Current research on female colour polymorphism in Ischnura damselflies suggests that a balanced fitness trade-off between morphotypes contributes to the maintenance of polymorphism inside populations. The genetic inheritance system constitutes a key factor to understand morph fluctuation and fitness. Ischnura genei, an endemic species of some Mediterranean islands, has three female colour morphs, including one androchrome (male-coloured) and two gynochromes. In this study, we reared two generations of I. genei under laboratory conditions and tested male behavioural responses to female colour morphs in the field. We recorded ontogenetic colour changes and studied morph frequency in three populations from Sardinia (Italy). Morph frequencies of laboratory crosses can be explained by a model based on an autosomal locus with three alleles and sex-restricted expression, except for one crossing of 42 families with unexpected offspring. The allelic dominance relationship was androchrome > infuscans > aurantiaca. Old individuals reared in the laboratory exhibited different levels of melanism in variable extent depending on sex and morph. Results of model presentations indicate a male preference for gynochrome females and the lack of recognition of androchromes as potential mates. Aurantiaca females were the most frequent morph in the field (63–87%). Further studies in other populations and islands are needed to understand the maintenance of this polymorphism

Variability in activity differs between castes in the ant Linepithema humile

1. The study of behavioural variability has a long research tradition in social insects. Because of their contribution to division of labour, between-individual variations have been mostly studied within the worker caste. In contrast, the level of behavioural variation between queens has been much less studied. 2. In ants, a high level of behavioural variability could contribute to the ecological success of invasive species by favouring the colonisation of new environments. 3. In the invasive ant species Linepithema humile (Mayr), we used a standardised test to assess plasticity and predictability in activity level between workers and queens. 4. We found that only queens, not workers, displayed between-individual variability in plasticity. 5. We propose that the behavioural variability of queens could be an asset favouring the adaptation of invasive ant species to changing environments

Variability in activity differs between castes in the ant Linepithema humile

International audience1. The study of behavioural variability has a long research tradition in social insects. Because of their contribution to division of labour, between-individual variations have been mostly studied within the worker caste. In contrast, the level of behavioural variation between queens has been much less studied. 2. In ants, a high level of behavioural variability could contribute to the ecological success of invasive species by favouring the colonisation of new environments. 3. In the invasive ant species Linepithema humile (Mayr), we used a standardised test to assess plasticity and predictability in activity level between workers and queens. 4. We found that only queens, not workers, displayed between-individual variability in plasticity. 5. We propose that the behavioural variability of queens could be an asset favouring the adaptation of invasive ant species to changing environments

Data from: Male biased sex ratio reduces the fecundity of one of three female morphs in a polymorphic damselfly

Females of the damselfly Ischnura graellsii display 3 color morphs, a male-like androchrome morph and 2 other morphs, infuscans and aurantiaca, which are not male-like. Previous research has suggested that male harassment has a negative effect on female fitness in many different insect species. Studying how male harassment affects fitness of the different female color morphs is key to a better understanding of how these morphs are maintained in natural populations. This study evaluated the response of female morphs of I. graellsii to contrasting sex ratios under controlled laboratory conditions. In our experiments, male abundance, through increased harassment, affected differentially the fecundity of females of the 3 color morphs. A male biased (3:1) sex ratio drastically decreased the average fecundity of infuscans females but had no effect on androchrome and aurantiaca females. Taking into account our results and previous studies that indicate that males prefer infuscans females, we propose a mechanism for the maintenance of this polymorphism. In this scenario, within-generation fluctuations in male abundance produce 2 regimes: One in which male abundance disfavors infuscans females by decreasing their fecundity and other in which a low male abundance results in androchromes that do not mate because of their low appeal to males. By studying a simple population genetics model, we found that the mechanism that we propose may contribute to maintain a stable female-limited polymorphism under a wide range of parameter combinations

Ontogenetic colour changes and male polymorphism in <i>Mnais andersoni</i> (Odonata: Calopterygidae)

<p>Colour-based traits are widespread in flying species due to the importance of visual perception in their communication. Ontogenetic colour changes and reversible physiological colours occur in some species and are used as communication signals to conspecifics. The genus <i>Mnais</i> (Zygoptera: Calopterygidae) shows both genetic colour polymorphism and age-related colour changes, making challenging even the identification of species. Here we study three Chinese populations of <i>Mnais andersoni</i> during one month by mark-resighting methods. We describe the ontogenetic body and wing colour changes of male morphs (orange-winged and hyaline-winged) and females. With maturity, thoracic colour changes from metallic green to copper. The initially transparent wings of the hyaline winged males and females became light amber with age, while the orange-winged males show this colour since emergence to maturity. Whitish pruinosity covered all thorax in orange-winged males, while it remained limited to the ventral part of the thorax in hyaline-winged males and females. Hyaline-winged males presented less abdominal pruinosity than the rest of individuals. Our observations suggest that male morphs of <i>M. andersoni</i> are analogous to other species of the genus.</p

Data from: Male biased sex ratio reduces the fecundity of one of three female morphs in a polymorphic damselfly

Females of the damselfly Ischnura graellsii display 3 color morphs, a male-like androchrome morph and 2 other morphs, infuscans and aurantiaca, which are not male-like. Previous research has suggested that male harassment has a negative effect on female fitness in many different insect species. Studying how male harassment affects fitness of the different female color morphs is key to a better understanding of how these morphs are maintained in natural populations. This study evaluated the response of female morphs of I. graellsii to contrasting sex ratios under controlled laboratory conditions. In our experiments, male abundance, through increased harassment, affected differentially the fecundity of females of the 3 color morphs. A male biased (3:1) sex ratio drastically decreased the average fecundity of infuscans females but had no effect on androchrome and aurantiaca females. Taking into account our results and previous studies that indicate that males prefer infuscans females, we propose a mechanism for the maintenance of this polymorphism. In this scenario, within-generation fluctuations in male abundance produce 2 regimes: One in which male abundance disfavors infuscans females by decreasing their fecundity and other in which a low male abundance results in androchromes that do not mate because of their low appeal to males. By studying a simple population genetics model, we found that the mechanism that we propose may contribute to maintain a stable female-limited polymorphism under a wide range of parameter combinations

Intraspecific variation in clutch size and maternal investment in pueriparous and larviparous Salamandra salamandra females

Amphibian reproductive modes are diverse and are characterised by complex adaptations, including vast variability in life history traits and different parental investment strategies. For instance, viviparity is rare in urodeles despite the potential ecological advantages gained in such populations by having semi-independency from water. The fire salamander, Salamandra salamandra, shows remarkable intraspecific variation in reproductive modes, with two strategies co-occurring: a common reproductive mode, larviparity (parturition of aquatic larvae), and a phylogenetically derived reproductive mode, pueriparity (parturition of terrestrial juveniles). Pueriparous populations of S. salamandra have at least two independent origins, the first originating from its northern distribution in the Iberian Peninsula, and the second at two insular populations on the northwestern Iberian coast. Here, we analyse the patterns of variability of some life-history traits in larviparous and pueriparous populations of S. salamandra, including pueriparous populations from the two independent origins, to understand how these traits relate to the evolutionary transitions in reproductive modes in S. salamandra. Our study shows differences in female body size and clutch and brood size between larviparous and pueriparous fire salamanders. We did not find differences in female investment between reproductive modes, and thus, the evolution to pueriparity in S. salamandra is likely characterised by the re-allocation of eggs to matrotrophy. Our study also confirms pueriparity and larviparity as the characteristic reproductive modes for insular and coastal/mainland S. s. gallaica populations, respectively, revealing the potential presence of pueriparity in one coastal population. This comparative analysis sheds light on the maternal factors that might have driven, or are related to, the evolution of pueriparity in this unique biological system and sets up the basis for testing different hypotheses that include climatic, ecological, physiological, and genetic factors as drivers of this evolutionary transition.This research also received support from the SYNTHESYS Project http://www.synthesys.info/ which is financed by European Community Research Infrastructure Action under the FP7 ‘‘Capacities’’ Programme at the Museo Museo Nacional de Ciencias Naturales (CSIC) (Ref: ES-TAF-1987).Peer reviewe

Data from: Integrating the pace-of-life syndrome across species, sexes and individuals: covariation of life history and personality under pesticide exposure

The pace-of-life syndrome (POLS) hypothesis integrates covariation of life-history traits along a fast–slow continuum and covariation of behavioural traits along a proactive–reactive personality continuum. Few studies have investigated these predicted life-history/personality associations among species and between sexes. Furthermore, whether and how contaminants interfere with POLS patterns remains unexplored. We tested for covariation patterns in life history and in behaviour, and for life-history/personality covariation among species, among individuals within species and between sexes. Moreover, we investigated whether pesticide exposure affects covariation between life history and behaviour and whether species and sexes with a faster POLS strategy have a higher sensitivity to pesticides. We reared larvae of four species of Ischnura damselflies in a common garden experiment with an insecticide treatment (chlorpyrifos absent/present) in the final instar. We measured four life-history traits (larval growth rate during the pesticide treatment, larval development time, adult mass and life span) and two behavioural traits (larval feeding activity and boldness, each before and after the pesticide treatment). At the individual level, life-history traits and behavioural traits aligned along a fast–slow and a proactive–reactive continuum, respectively. Species-specific differences in life history, with fast-lived species having a faster larval growth and development, a lower mass at emergence and a shorter life span, suggested that time constraints in the larval stage were predictably driving life-history evolution both in the larval stage and across metamorphosis in the adult stage. Across species, females were consistently more slow-lived than males, reflecting that a large body size and a long life span are generally more important for females. In contrast to the POLS hypothesis, there was only little evidence for the expected positive coupling between life-history pace and proactivity. Pesticide exposure decreased larval growth rate and affected life-history/personality covariation in the most fast-lived species. Our study supports the existence of life-history and behavioural continua with limited support for life-history/personality covariation. Variation in digestive physiology may explain this decoupling of life history and behaviour and provide valuable mechanistic insights to understand and predict the occurrence of life-history/personality covariation patterns

Genetic divergence and aggressiveness within a supercolony of the invasive ant Linepithema humile

Biological invasions constitute an opportunity to study the evolutionary processes behind species’ adaptations. The invasive potential of some species, like the Argentine ant (Linepithema humile), has likely been increasing because they show low intraspecific competition. However, multiple introductions over time or genetic divergence could increase the probability of intraspecific competition, constituting barriers for their dispersal and thus, decreasing invasive success. Here, we studied the genetic and behavioural variability of L. humile workers collected at six locations on the NW coast of the Iberian Peninsula, a possible scenario for multiple introductions and population divergence, due to its high level of maritime traffic and complex coastal geography. We analysed behaviours related to spatial navigation (exploration, wall-following), resources acquisition, and competition (inter and intraspecific aggressiveness) through two relevant seasons for the nest ecology: spring and autumn. Genetic analyses using microsatellites indicated that the nests studied belonged to the most spread supercolony in South Europe. However, we identified the existence of two genetically differentiated clusters in Galiza. Lethal interactions were found between workers from different and similar genetic clusters, but a trend suggests higher agonistic behaviours between the two genetic groups. Genetic differences were positively correlated with the geographical distance, but aggressiveness was not correlated with any of them. Ants from each of the tested nests expressed different behaviours with high plasticity through time. Ants from all nests showed more exploration and aggressiveness, less wall-following and faster detection of food in autumn than in spring, with no intraspecific aggressiveness observed in spring. Our findings suggest competition between nests of the same supercolony and behavioural seasonal variability, supporting the hypothesis of divergent evolutionary processes. The results of our work question the assumed unity of supercolonies of this species and offer insights for understanding the future adaptation of L. humile in the introduced areas