Sexual signaling and speciation,a microevolutionary perspective

Despite the growing evidence that sexual selection can drive speciation, the evolution of sexual signals in natural populations is far from being well-understood. Sexual signals evolve in response to a variety of factors. Some of the most important selective factors are conspecifics, transmission efficiency in a particular environment, detection by predators, and phylogenetic constraints. These factors have been addressed quite successfully in studies of single types of signals in both vertebrates and invertebrates. However, it is less clear how multimodal signals evolve because the factors listed above will act on every component of the signaling system, and the relative weights of each type of signal must be taken into account. Species of Drosophila are excellent for such analyses because they are amenable to both phenotypic experimentation and genetic manipulation. This paper presents an approach that involves two analyses: studies of which signals are sexually selected within a species, and parallel studies of the signals that are involved in behavioral isolation between closely related species. If the same signal characteristics are involved in both processes, they would provide support for the hypothesis that sexual selection can drive speciation. This approach is illustrated with studies of Hawaiian Drosophila and a review of signals that could be sexually selected in Drosophila melanogaster.     

Personality-specific carry-over effects on breeding

Carry-over effects describe the phenomenon whereby an animal''s previous conditions influence its subsequent performance. Carry-over effects are unlikely to affect individuals uniformly, but the factors modulating their strength are poorly known. Variation in the strength of carry-over effects may reflect individual differences in pace-of-life: slow-paced, shyly behaved individuals are thought to favour an allocation to self-maintenance over current reproduction, compared to their fast-paced, boldly behaved conspecifics (the pace-of-life syndrome hypothesis). Therefore, detectable carry-over effects on breeding should be weaker in bolder individuals, as they should maintain an allocation to reproduction irrespective of previous conditions, while shy individuals should experience stronger carry-over effects. We tested this prediction in black-legged kittiwakes breeding in Svalbard. Using miniature biologging devices, we measured non-breeding activity of kittiwakes and monitored their subsequent breeding performance. We report a number of negative carry-over effects of non-breeding activity on breeding, which were generally stronger in shyer individuals: more active winters were followed by later breeding phenology and poorer breeding performance in shy birds, but these effects were weaker or undetected in bolder individuals. Our study quantifies individual variability in the strength of carry-over effects on breeding and provides a mechanism explaining widespread differences in individual reproductive success.     

Cross fostering in mice: behavioral and physiological carry-over effects in adulthood

Cross fostering is a widely used laboratory practice. However, relatively few studies have directly investigated the carry-over effects of this procedure in adult animals. The aim of the present study is to investigate the late effects of cross fostering (CF) at birth (in litters composed of no siblings) on adult mice. When adults, cross-fostered male and female mice were examined for intrasex aggression, and levels of emotionality, exploration and anxiety. In addition, body weight was monitored, several internal organs were weighed and plasma corticosterone levels were measured. When compared to controls, body weight of CF male and female mice was increased, at least after early puberty. CF males showed smaller preputial glands, while basal corticosterone level was not affected by cross fostering. In the free-exploratory test, CF males, but not females, showed a behavioral profile suggestive of lower anxiety. These effects in adulthood cannot be ascribed to differences in the maternal care received, which was not affected by cross fostering. In conclusion, cross fostering at birth induced a number of behavioral and physiological alterations in mice, particularly in males. These findings should be carefully evaluated when applying cross fostering procedure to laboratory animals.     

Sexual signaling and immune function in the black field cricket Teleogryllus commodus

The immunocompetence handicap hypothesis predicts that male sexual trait expression should be positively correlated with immunocompetence. Here we investigate if immune function in the cricket, Teleogryllus commodus, is related to specific individual components of male sexual signals, as well as to certain multivariate combinations of these components that females most strongly prefer. Male T. commodus produce both advertisement and courtship calls prior to mating. We measured fine-scale structural parameters of both call types and also recorded nightly advertisement calling effort. We then measured two standard indices of immune function: lysozyme-like activity of the haemolymph and haemocyte counts. We found a weak, positive relationship between advertisement calling effort and lysozyme-like activity. There was, however, little evidence that individual structural call components or the net multivariate attractiveness of either call type signalled immune function. The relationships between immunity and sexual signaling did not differ between inbred and outbred males. Our data suggest that it is unlikely that females assess overall male immune function using male calls.     

Predicting the consequences of carry-over effects for migratory populations

Migratory animals present a unique challenge for predicting population size because they are influenced by events in multiple stages of the annual cycle that are separated by large geographic distances. Here, we develop a model that incorporates non-fatal carry-over effects to predict changes in population size and show how this can be integrated with predictive models of habitat loss and deterioration. Examples from Barn swallows, Greater snow geese and American redstarts show how carry-over effects can be estimated and integrated into the model. Incorporation of carry-over effects should increase the predictive power of models. However, the challenge for developing accurate predictions rests both on the ability to estimate parameters from multiple stages of the annual cycle and to understand how events between these periods interact to influence individual success.     

Sexual signaling in the European bitterling: females learn the truth by direct inspection of the resource

In many taxa females appear to base their mate choice on multipletraits. But the relative importance of different traits inmate choice has rarely been determined. Here we show that femalesof a freshwater fish, the European bitterling, Rhodeus sericeus,base their mate choice on multiple traits that differ in theirreliability as indicators of expected reproductive successand are used at different stages of the decision process. Theinitial decision to inspect a male is based on male behaviorand red coloration, whereas the final spawning decision isbased on the quality of the live unionid mussel, Anodonta anatina,that the male is defending as an oviposition site. Male traitsmay indicate which males are worth inspecting by reflectingmale quality, such as reproductive condition and genetic constitution.Male traits do not, however, reflect mussel quality, as bright males also court females vigorously toward mussels that yielda low probability of survival of the offspring. Females, onthe other hand, are choosier than males in their choice ofspawning site and seem to gain reliable information about thesurvival probability of the eggs by inspecting the mussel directly.     

The crisis of the thesis of climatic pessimism: malaria and the climatic question

The publication of Boudin's Traité de Geographie et de Statistique médicale (1857) and the creation in 1908 of the Institut de Pathologie Exotique by Laveran, correspond to two entirely different manners of considering tropical diseases and adaptability (or acclimatation) to the Tropics, directly associated with the idea of capability or incapability of Europeans to resist tropical diseases. We analyse the way perspectives have changed with respect to the influence that climate, particularly tropical, exert on the body of individuals and on populations used to live under temperate climatic conditions. The manner the concepts of medical geography, climatic pessimism and individual acclimatation get articulated with the discovery of tropical diseases, their aetiological agents and their localisation, particularly malaria, can only be understood by also analysing how the problems generated by the diversity of races and migration phenomena have been envisaged.     

Sexual dimorphism in club cell distribution in the European minnow and immunocompetence signaling

Female minnows Phoxinus phoxinus have eight times as many club cells as males in their dorsal skin during the breeding season. The distribution of these cells is androgen sensitive and they may have an antipathogenic function. Since androgens also stimulate development of secondary sexual characters and depresses the immune system the putative role of nuptial coloration as a signal about immune function is discussed.     

Embryonic learning and developmental carry-over effects in an invasive anuran

Carry-over effects influence trait responses in later life stages as a result of early experience with environmental cues. Predation risk is an influential stressor and selection exists for early recognition of threats. In particular, invasive species may benefit from carry-over effects by preemptively recognizing and responding to novel predators via latent developmental changes and embryonic learning. In a factorial experiment, we conditioned invasive American bullfrog embryos (Lithobates catesbeianus) to the odor of a novel fish predator, largemouth bass (Micropterus salmoides) alone or in combination with injured conspecific cues. We quantified developmental carryover in the larval life stage and found that individuals conditioned to the highest risk (fish and injured conspecific cues) grew into longer bodied larvae relative to larvae from lower risk treatments. We also assessed embryonic learning, a behavioral carry-over effect, and found an interaction between embryonic conditioning and larval exposure. Behavioral responses were only found in scenarios when predation risk varied in intensity across life history stages, thus requiring a more flexible antipredator strategy. This indicates a potential trade-off between the two strategies in larval growth and development rates, and time until metamorphosis. Our results suggest that early predator exposure and carry-over effects have significant impacts on life history trajectories for American bullfrogs. This research contributes to our understanding of a potentially important invasion mechanism in an anuran species of conservation concern.     

Evaluation of tebufenozide carry-over and residual effects on spruce budworm (Lepidoptera: Tortricidae)

Laboratory and field studies investigated carry-over effects of tebufenozide on spruce budworm, Choristoneura fumiferana (Clemens). In the laboratory, third and fourth instars were fed either sublethal doses of tebufenozide (10 ppm) or water onAbies balsamea (L.) Mill. needles, reared to adulthood and allowed to oviposit on laying surfaces 1 or 14 d after being sprayed with water or tebufenozide concentrations of 17.5, 35.0, and 70.0 g/liter. Percentage adult emergence and sex ratio were not affected by larval ingestion of the tebufenozide. Also, the mean number of eggs laid on untreated wax paper by moths reared from tebufenozide-treated larvae was similar to the controls. Hence, tebufenozide did not inhibit carry-over effects on treated larvae. Oviposition on tebufenozide-treated wax paper by moths reared from untreated larvae was affected by both the substrate concentration and the age of the treatment residue. When offered treated and untreated laying surfaces simultaneously, C. fumiferana did not show a preference. However, significantly fewer eggs were laid on both laying surfaces by fewer females than when tebufenozide was absent. Residual tebufenozide on wax paper did not affect egg hatch but topical applications were toxic to eggs. Field studies appear to corroborate laboratory results and suggest that although the ingestion of tebufenozide by larval spruce budworm might not impair adult reproduction, the insecticide's presence in the environment could inhibit oviposition. This inhibition was considered to be a primary factor in tebufenozide's multi-year effects against spruce budworm populations.     

Cytokine signaling: Cytokine-inducible signaling inhibitors

Seven members of a family of cytokine-inducible proteins have been identified, a number of which have been shown to act as negative regulators of cytokine action. All of these proteins contain a central Src homology 2 domain, as well as conserved motifs in their carboxy-terminal regions.     

Reproductive strategy and carry-over effects for species with complex life histories

We investigated the influences of natal-pool and metamorph characteristics on juvenile survival, age-specific breeding probabilities, and dispersal of wood frogs (Lithobates sylvatica) and used this information to infer how life history strategies of short-lived species may offset risks associated with breeding in highly variable habitats. We used multistate mark-recapture data from eight wood frog populations in Maryland, USA, to investigate the influences of natal-pond and metamorph characteristics on post-metamorphic demographics. We found that post-metamorphic juvenile survival was highly variable and negatively influenced by abiotic conditions experienced during development but showed little relationship to larval density or size at metamorphosis. Estimates of recruitment and dispersal probabilities indicated that males mature earlier than females, and a small percentage of each sex disperse to non-natal pools. Survival probabilities for adults during the non-breeding season were less variable than juvenile rates, lower for females, and negatively related to mean monthly precipitation. Survival of adults during the breeding season was generally very high. We provide the first robust estimates of post-metamorphic vital rates of wood frogs that allow for variation in capture probabilities. We found little evidence for an effect of metamorph traits on juvenile survival, suggesting that wood frogs may be able to overcome initial disadvantages to have similar post-metamorphic performance. Our study suggests that variation in the age of maturity for wood frogs may mitigate risks associated with breeding in a highly variable habitat to maximize lifetime fitness without increasing lifespan, and this strategy is minimally affected by carry-over effects from the larval stage.     

Evidence for carry-over effects of predator exposure on pathogen transmission potential

Accumulating evidence indicates that species interactions such as competition and predation can indirectly alter interactions with other community members, including parasites. For example, presence of predators can induce behavioural defences in the prey, resulting in a change in susceptibility to parasites. Such predator-induced phenotypic changes may be especially pervasive in prey with discrete larval and adult stages, for which exposure to predators during larval development can have strong carry-over effects on adult phenotypes. To the best of our knowledge, no study to date has examined possible carry-over effects of predator exposure on pathogen transmission. We addressed this question using a natural food web consisting of the human malaria parasite Plasmodium falciparum, the mosquito vector Anopheles coluzzii and a backswimmer, an aquatic predator of mosquito larvae. Although predator exposure did not significantly alter mosquito susceptibility to P. falciparum, it incurred strong fitness costs on other key mosquito life-history traits, including larval development, adult size, fecundity and longevity. Using an epidemiological model, we show that larval predator exposure should overall significantly decrease malaria transmission. These results highlight the importance of taking into account the effect of environmental stressors on disease ecology and epidemiology.     

Brain plasticity over the metamorphic boundary: carry-over effect of larval environment on froglet brain development

Brain development shows high plasticity in response to environmental heterogeneity. However, it is unknown how environmental variation during development may affect brain architecture across life history switch points in species with complex life cycles. Previously, we showed that predation and competition affect brain development in common frog (Rana temporaria) tadpoles. Here, we studied whether larval environment had carry-over effects in brains of metamorphs. Tadpoles grown at high density had large optic tecta at metamorphosis, whereas tadpoles grown under predation risk had small diencephala. We found that larval density had a carry-over effect on froglet optic tectum size, whereas the effect of larval predation risk had vanished by metamorphosis. We discuss the possibility that the observed changes may be adaptive, reflecting the needs of an organism in given environmental and developmental contexts.     

Habitat distribution models for intertidal seaweeds: responses to climatic and non‐climatic drivers

Aim Because intertidal organisms often live close to their physiological tolerance limits, they are potentially sensitive indicators of climate‐driven changes in the environment. The goals of this study were to assess the effect of climatic and non‐climatic factors on the geographical distribution of intertidal macroalgae, and to predict future distributions under different climate‐warming scenarios. Location North‐western Iberian Peninsula, southern Europe. Methods We developed distribution models for six ecologically important intertidal seaweed species. Occurrence and microhabitat data were sampled at 1‐km² resolution and analysed with climate variables measured at larger spatial scales. We used generalized linear models and applied the deviance and Bayesian information criterion to model the relationship between environmental variables and the distribution of each target species. We also used hierarchical partitioning (HP) to identify predictor variables with higher independent explanatory power. Results The distributions of Himanthalia elongata and Bifurcaria bifurcata were correlated with measures of terrestrial and marine climate, although in opposite directions. Model projections under two warming scenarios indicated the extinction of the former at a faster rate in the Cantabrian Sea (northern Spain) than in the Atlantic (west). In contrast, these models predicted an increase in the occurrence of B. bifurcata in both areas. The occurrences of Ascophyllum nodosum and Pelvetia canaliculata, species showing rather static historical distributions, were related to specific non‐climatic environmental conditions and locations, such as the location of sheltered sites. At the southernmost distributional limit, these habitats may present favourable microclimatic conditions or provide refuges from competitors or natural enemies. Model performances for Fucus vesiculosus and F. serratus were similar and poor, but several climatic variables influenced the occurrence of the latter in the HP analyses. Main conclusions The correlation between species distributions and climate was evident for two species, whereas the distributions of the others were associated with non‐climatic predictors. We hypothesize that the distribution of F. serratus responds to diverse combinations of factors in different sections of the north‐west Iberian Peninsula. Our study shows how the response of species distributions to climatic and non‐climatic variables may be complex and vary geographically. Our analyses also highlight the difficulty of making predictions based solely on variation in climatic factors measured at coarse spatial scales.