The role of temperature and larval crowding in morph determination in a tropical beetle, Callosobruchus subinnotatus

Many insect species can produce individuals of more than one form or morph. Different morphs of the same species may differ in their physiology, morphology and in behaviour. Understanding the factors and mechanisms involved in determining the production of different morphs of insect species is of major importance in understanding the evolution of specific life-history strategies. In this paper, we studied the importance of temperature as an environmental factor involved in morph determination of the tropical beetle, Callosobruchus subinnotatus. Adults occur as relatively sedentary, highly fecund, 'normal' morphs or as an 'active' morph adapted to dispersal. Larval crowding, seed density and external temperature were independently manipulated in a series of controlled experiments and the proportions of 'active' and 'normal' adult morphs among the emergent adult populations were quantified and compared. Development in crowded conditions was found to be associated with the production of a significantly higher proportion of 'active' adults than development in isolation, and was also responsible for a predictable rise in the localised temperature of infested heaps of seeds of between 4 and 8 degrees C above ambient (27 degrees C). This rise in temperature is subsequently shown to be directly and quantitatively associated with the proportion of 'active' adults among emerging adults, both in the presence of larval crowding and independently from it. Thus, it is suggested that in the crowded environment representative of an infested seed store, it is rising temperature, occurring at a specific point in insect development which is the proximate cue for 'active' morph induction in C. subinnotatus. The results are compared to the strategies used by other polymorphic insects to survive in heterogeneous environments.     

Morph‐dependent fitness and directional change of morph frequencies over time in a Dutch population of Common buzzards Buteo buteo

How genetic polymorphisms are maintained in a population is a key question in evolutionary ecology. Previous work on a plumage colour polymorphism in the common buzzard Buteo buteo suggested heterozygote advantage as the mechanism maintaining the co‐existence of three morphs (light, intermediate and dark). We took advantage of 20 years of life‐history data collected in a Dutch population to replicate earlier studies on the relationship between colour morph and fitness in this species. We examined differences between morphs in adult apparent survival, breeding success, annual number of fledglings produced and cumulative reproductive success. We found that cumulative reproductive success differed among morphs, with the intermediate morph having highest fitness. We also found assortative mating for colour morph, whereby assortative pairs were more likely to produce offspring and had longer‐lasting pair bonds than disassortative pairs. Over the 20‐year study period, the proportion of individuals with an intermediate morph increased. This apparent evolutionary change did not just arise from selection on individual phenotypes, but also from fitness benefits of assortative mating. The increased frequency of intermediates might also be due to immigration or drift. We hypothesize that genetic variation is maintained through spatial variation in selection pressures. Further studies should investigate morph‐dependent dispersal behaviour and habitat choice.     

Telomere length in relation to colour polymorphism across life stages in the tawny owl

Telomere erosion has been proposed to be tightly associated with senescence, environmental stressors and life history trade‐offs. How telomere dynamics vary across life stages and especially in relation to (heritable) phenotypic traits is still unclear. The tawny owl Strix aluco display a highly heritable melanin‐based colour polymorphism, a grey and a brown morph, linked to several fitness traits including morph‐specific telomere dynamics. As adults, brown tawny owls have shorter relative telomere length (RTL) and exhibit faster telomere shortening rate than grey owls. Here we test if these morph‐specific telomere dynamics emerge already during growth, or if they are induced only in adult life through differential physiological costs associated with the life history of the morphs. We analysed RTL from 287 tawny owl offspring and 81 first breeding adults to evaluate at what life stage morph‐specific patterns emerge. We found no differences in RTL between the two morphs during the nestling period nor at the first breeding attempt. Sex, brood size or size rank in the nest did not affect offspring RTL. Among first‐breeders, females had shorter telomeres than males suggesting a sampling‐time dependent difference in reproductive costs between sexes, due to the prominent sex roles in tawny owls in the early nestling period. The probability to return to breed after the first breeding attempt was not affected by RTL, sex or colour morph. The lack of morph‐specific difference in RTL among nestlings and first breeders suggests that previously observed morph‐specific differences in RTL dynamics in adults emerge at the onset of the breeding career and is likely due to different physiological profiles and life‐history strategies adopted by adults. We conclude that different telomere dynamics and senescence patterns among highly heritable phenotypes (colour morphs) are likely to be a result of differential costs of reproduction and self‐maintenance.     

Differentiation in a tropical deceptive orchid: colour polymorphism and beyond

Colour polymorphism has often been described among individuals of deceptive orchid species, and several studies have investigated reproductive success variations among colour morphs. However, whether colour morphs differed in other traits has received little attention in previous studies. Here, we report the case of a tropical deceptive orchid in Reunion Island that exhibits three different colour varieties. We investigated patterns of trait variation among colour varieties and found significant differences in floral and inflorescence morphology. Interestingly, we found that most populations included only individuals of a single variety, and that strong differences exist among varieties in spatial distribution and flowering phenology. This situation differs from previously reported cases of floral polymorphism in deceptive orchids where colour morphs co-occur and flower in the same populations. The spatio-temporal variation in flowering suggests that colour varieties have independent reproductive ecologies and are adapted to local conditions. We propose that potential variations in pollinator species abundance or diversity and the co-occurrence of nectar-producing species in the community may have driven the adaptation of each variety to its current pollination niche.     

Behavioral and hormonal correlates of alternative reproductive strategies in a polygynous lizard: Tests of the relative plasticity and challenge hypotheses

Species with alternative reproductive tacts are good models to investigate the poorly understood question of whether individual variation within sexes results from the same physiological mechanisms that control variation between sexes. We have shown previously that adult male tree lizards, Urosaurus ornatus, of different throat color morphs express different levels of aggression in the laboratory. Further field results support the suggestion that the two morphs practice alternative reproductive tactics because the two morphs express different levels of aggressive behavior under field conditions and exhibit dramatic and opposite responses to aggressive challenges. However, despite these behavioral differences, the two morphs do not differ in levels of testosterone or corticosterone either in undisturbed situations or following aggressive challenge. These results are consistent with the relative plasticity hypothesis which proposes that organizational, rather than activational, actions of steroid hormones will be more important in morph differentiation when morphs are fixed in adult life, as they are in tree lizards. These results also support the hypothesis that steroid hormonal levels are insensitive to social modulation in males of species such as U. ornatus without paternal care.     

Extensive genetic differentiation between recently evolved sympatric Arctic charr morphs

The availability of diverse ecological niches can promote adaptation of trophic specializations and related traits, as has been repeatedly observed in evolutionary radiations of freshwater fish. The role of genetics, environment, and history in ecologically driven divergence and adaptation, can be studied on adaptive radiations or populations showing ecological polymorphism. Salmonids, especially the Salvelinus genus, are renowned for both phenotypic diversity and polymorphism. Arctic charr (Salvelinus alpinus) invaded Icelandic streams during the glacial retreat (about 10,000 years ago) and exhibits many instances of sympatric polymorphism. Particularly, well studied are the four morphs in Lake Þingvallavatn in Iceland. The small benthic (SB), large benthic (LB), planktivorous (PL), and piscivorous (PI) charr differ in many regards, including size, form, and life history traits. To investigate relatedness and genomic differentiation between morphs, we identified variable sites from RNA‐sequencing data from three of those morphs and verified 22 variants in population samples. The data reveal genetic differences between the morphs, with the two benthic morphs being more similar and the PL‐charr more genetically different. The markers with high differentiation map to all linkage groups, suggesting ancient and pervasive genetic separation of these three morphs. Furthermore, GO analyses suggest differences in collagen metabolism, odontogenesis, and sensory systems between PL‐charr and the benthic morphs. Genotyping in population samples from all four morphs confirms the genetic separation and indicates that the PI‐charr are less genetically distinct than the other three morphs. The genetic separation of the other three morphs indicates certain degree of reproductive isolation. The extent of gene flow between the morphs and the nature of reproductive barriers between them remain to be elucidated.     

Yellow mutant of the Neotropical green lacewing Chrysoperla externa: trait inheritance and predator performance

The Neotropical green lacewing Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) is a key predator of various small soft‐bodied pest species. Chrysopidae species are known as ‘green lacewings’ due to their overall green body coloration. However, yellow mutant individuals were observed emerging from our lacewing rearing colony. Thus, the mode of inheritance of the yellow trait was studied and the hypothesis of an autosomal recessive allele for yellow color was tested using hybridization and backcrossing techniques. Furthermore, the possible implications of this color variation on specific life‐history characteristics of C. externa and the predation rates of each morph were evaluated. In both yellow and green morphs, basic life‐history characteristics were monitored, including time to hatching and viability of eggs, duration, and viability of larval and pupal stages, emergence rate and survivorship of adults, and fecundity and longevity of females. The yellow and green morphs were indistinguishable with respect to all life‐history traits evaluated and the predation rate of their larvae. Crossing experiments revealed the yellow color to be caused by a homozygous recessive allele, without sex‐linked expression. We conclude that the allele for yellow color is occurring at high frequency in the laboratory colony, supporting the existence of a genetic polymorphism for body ground color.     

Correlated morphological and colour differences among females of the damselfly Ischnura elegans

Abstract 1. The female‐limited colour polymorphic damselfly Ischnura elegans has proven to be an interesting study organism both as an example of female sexual polymorphism, and in the context of the evolution of colour polymorphism, as a model of speciation processes. 2. Previous research suggests the existence of correlations between colour morph and other phenotypic traits, and the different female morphs in I. elegans may be pursuing alternative phenotypically integrated strategies. However, previous research on morphological differences in southern Swedish individuals of this species was only carried out on laboratory‐raised offspring from a single population, leaving open the question of how widespread such differences are. 3. The present study therefore analysed multi‐generational data from 12 populations, investigating morphological differences between the female morphs in the field, differences in the pattern of phenotypic integration between morphs, and quantified selection on morphological traits. 4. It was found that consistent morphological differences indeed existed between the morphs across populations, confirming that the previously observed differences were not simply a laboratory artefact. It was also found, somewhat surprisingly, that despite the existence of sexual dimorphism in body size and shape, patterns of phenotypic integration differed most between the morphs and not between the sexes. Finally, linear selection gradients showed that female morphology affected fecundity differently between the morphs. 5. We discuss the relevance of these results to the male mimicry hypothesis and to the existence of potential ecological differences between the morphs.     

The cost of being able to fly: a study of wing polymorphism in two species of crickets

Summary The widespread occurrence of wing polymorphisms in insects suggests that the possession of wings and ability to fly adversely affect components of the insect's life characteristics that contribute to its Darwinian fitness. This hypothesis was tested by an analysis of the differences in life history parameters of the macropterous and micropterous morphs of the two cricket species G. firmus and A. fasciatus. In both species there were no differences in development time or adult survival between the two morphs. Significant differences in head width were not consistent between the two species but in both sexes of G. firmus and females of A. fasciatus (insufficient males for analysis) long-winged individuals weighed more than short-winged individuals with the same head width. In both species egg production is delayed in macropterous females. The cumulative fecundity of the micropterous morph is greater than the macropterous morph in both species but only in G. firmus is the difference statistically significant. A. fasciatus frequently loose their wings but no such loss has been observed in G. firmus. There is a significant increase in egg production after the loss of the wings. These results are in accord with those of Tanaka (1976) for the cricket, Pteronemobius taprobanensis.Breeding experiments indicate that in G. firmus the wing polymorphism is under genetic control. The decrease in fecundity is sufficiently large that genotypes producing only macropterous offspring could only persist in highly unstable environments where continuous dispersal was imperative for survival. However, the reproductive cost of a genotype producing a small percentage of macropterous individuals is slight. The fitness that accrues to a genotype producing a few dispersing offspring is likely to offset the small reproductive cost and hence wing polymorphisms should be favoured.     

Temperature drives pre‐reproductive selection and shapes the biogeography of a female polymorphism

Conflicts of interests between males and females over reproduction is a universal feature of sexually reproducing organisms and has driven the evolution of intersexual mimicry, mating behaviours and reproductive polymorphisms. Here, we show how temperature drives pre‐reproductive selection in a female colour polymorphic insect that is subject to strong sexual conflict. These species have three female colour morphs, one of which is a male mimic. This polymorphism is maintained by frequency‐dependent sexual conflict caused by male mating harassment. The frequency of female morphs varies geographically, with higher frequency of the male mimic at higher latitudes. We show that differential temperature sensitivity of the female morphs and faster sexual maturation of the male mimic increases the frequency of this morph in the north. These results suggest that sexual conflict during the adult stage is shaped by abiotic factors and frequency‐independent pre‐reproductive selection that operate earlier during ontogeny of these female morphs.     

Clutch size and reproductive success in a female polymorphic insect

Differences in reproductive success (RS) between different groups of individuals are of interest to researchers studying natural and sexual selection. Since it is often not feasible to quantify RS in the wild, researchers make use of proxies instead. One such proxy is clutch size. However, research on species providing parental care (mainly birds and mammals) has learned that a large clutch size does not guarantee a large number of offspring. In contrast, much less is known on the link between clutch size and RS for species lacking parental care, such as many reptiles and insects. Here, we ask whether clutch size provides a satisfactory estimate of RS for a polymorphic insect. Our study species is a damselfly showing two distinct female morphs for which RS (estimated by clutch size) has been studied to evaluate the evolutionary role of sexual conflict. However, in this system not only among family variation in offspring viability, but also differences between female morphs, may affect how clutch size relates to offspring number and quality. To evaluate the use of clutch size as estimate of RS, we examined how clutch size correlated with subsequent success measures of developing offspring by rearing damselfly from eggs to adults under two laboratory food treatments. In both treatments, we detected that clutch size correlated well with offspring number early in larval life, but that this relation is reduced by among family variation in survival in later developmental stages. Clutch size was moderately correlated with the number of offspring that successfully metamorphosed to winged adults. Patterns did not differ between female morphs and the nature of the correlation could not be explained from offspring quantity-quality trade-offs.     

Variability in diapause duration in the chestnut weevil: mixed ESS,genetic polymorphism or bet‐hedging?

Within-generation variability in diapause duration can be viewed either as a mixed Evolutionary Stable Strategy (ESS), a genetic polymorphism of pure strategies, or as bet-hedging. Diapause variability expressed by a single genotype that maximizes mean geometric fitness at the cost of mean arithmetic fitness is a bet-hedging strategy. Bet-hedging differs from mixed ESS and stable genetic polymorphism of pure strategies because in these latter the expected pay-offs for all phenotypes are equal. In insects, individuals with a prolonged diapause (long cycle) lose at least one reproductive opportunity and suffer lower survival before reproduction than those with a short diapause (short cycle). If long-cycle individuals compensate this cost by better adult performance, the compensation leads to a trade-off which could result in mixed ESS or genetic polymorphism of pure strategies since the overall fitness of the two morphs may be similar. In this paper, we show that in the chestnut weevil Curculio elephas adult performance, measured as sex ratio, longevity, weight, and realized fecundity of females, are similar in individuals emerged after one and two years. Long-cycle morphs emerge slightly before short-cycle ones but this eventual advantage for fertility probably does not compensate higher larval mortality and missed reproductive opportunity in long-cycle phenotypes. Therefore, the cost associated with prolonged diapause cannot be completely compensated for by a better adult performance. From these results, and previous data, we conclude that variability in diapause duration cycle is better explained as bet-hedging than mixed ESS or genetic polymorphism of pure strategies.     

An experimental test for alternative reproductive strategies underlying a female-limited polymorphism

Polymorphism often corresponds to alternative mating tactics in males, but much less is known about this relationship in females. However, recent work suggests that selection for alternative reproductive strategies in females can maintain genetic variation in important life-history traits. Brown anole lizards (Anolis sagrei) exhibit a genetically based polymorphism in dorsal pattern that is expressed only by females, which occur in bar (B), diamond (D) and intermediate diamond-bar (DB) morphs. Here, we use a combination of natural history data, captive breeding studies and phenotypic manipulations of reproductive investment to test the hypothesis that this polymorphism corresponds to morph-specific patterns of reproductive investment. Three years of data from wild females and two generations of captive breeding revealed no differences among morphs in the frequency of egg production or in the number, frequency, size or sex ratio of offspring. Manipulations of reproductive investment via surgical ovariectomy revealed significant costs of reproduction with respect to survival, growth, immune function and haematocrit, but the magnitudes of these costs did not differ among morphs. Collectively, our results refute the hypothesis that this sex-limited polymorphism is maintained by selection for alternative reproductive strategies. We compare this finding to other systems in which polymorphic females exhibit alternative reproductive tactics and discuss other selective factors that could maintain polymorphism in anoles.     

Disassortative mating and the maintenance of sexual polymorphism in painted maple

Since Darwin's pioneering research on plant reproductive biology (e.g. Darwin 1877), understanding the mechanisms maintaining the diverse sexual strategies of plants has remained an important challenge for evolutionary biologists. In some species, populations are sexually polymorphic and contain two or more mating morphs (sex phenotypes). Differences in morphology or phenology among the morphs influence patterns of non-random mating. In these populations, negative frequency-dependent selection arising from disassortative (intermorph) mating is usually required for the evolutionary maintenance of sexual polymorphism, but few studies have demonstrated the required patterns of non-random mating. In the current issue of Molecular Ecology, Shang et al. (2012) make an important contribution to our understanding of how disassortative mating influences sex phenotype ratios in Acer pictum subsp. mono (painted maple), a heterodichogamous, deciduous tree of eastern China. They monitored sex expression in 97 adults and used paternity analysis of open-pollinated seed to examine disassortative mating among three sex phenotypes. Using a deterministic 'pollen transfer' model, Shang et al. present convincing evidence that differences in the degree of disassortative mating in progeny arrays of the sex phenotypes can explain their uneven frequencies in the adult population. This study provides a useful example of how the deployment of genetic markers, demographic monitoring and modelling can be integrated to investigate the maintenance of sexual diversity in plants.     

九香虫形态及生物学特征研究

通过建立网室近自然实验种群,结合野生个体观察记述了云南玉溪九香虫Coridius chinensis (Dallas)种群的各虫期形态特征、在云南玉溪红塔区的年生活史、寄主范围、取食偏好、成虫及若虫的行为习性,为该虫的保育和规模化养殖提供依据。结果显示,九香虫卵有绿色和粉色两种生态型,若虫有5个龄期;在云南玉溪红塔区1年仅发生1代,仅以成虫态越冬;红塔区九香虫野生个体主要以佛手瓜和南瓜等葫芦科植物为食;取食偏好选择试验表明该虫最喜取食葫芦,冬瓜和南瓜次之;雌雄成虫可多次交配多次产卵,单雌单次平均产卵量为16.3±6.0粒。研究表明,云南玉溪红塔区的九香虫种群为典型的一化性昆虫,休眠期可达8个月;该虫食性较广,可取食多科植物,但以葫芦科瓜类为主;羽化成虫每年9月中旬至10月上旬陆续从佛手瓜、南瓜等寄主植物上迁至枯树皮下、柴堆等隐蔽场所越冬,翌年4月下旬陆续解除休眠,迁至佛手瓜、南瓜等作物上取食繁殖。     

Cardiovascular system in larval zebrafish responds to developmental hypoxia in a family specific manner

Background

In eastern North America two common colour morphs exist in most populations of redback salamanders (Plethodon cinereus). Previous studies have indicated that the different morphs may be adapted to different thermal niches and the morphological variation has been linked to standard metabolic rate at 15°C in one population of P. cinereus. It has therefore been hypothesized that a correlated response to selection on metabolic rate across thermal niches maintains the colour polymorphism in P. cinereus. This study tests that hypothesis.

Results

We found that the two colour morphs do sometimes differ in their maintenance metabolic rate (MMR) profiles, but that the pattern is not consistent across populations or seasons. We also found that when MMR profiles differ between morphs those differences do not indicate that distinct niches exist. Field censuses showed that the two colour morphs are sometimes found at different substrate temperatures and that this difference is also dependent on census location and season.

Conclusion

While these morphs sometimes differ in their maintenance energy expenditures, the differences in MMR profile in this study are not consistent with maintenance of the polymorphism via a simple correlated response to selection across multiple niches. When present, differences in MMR profile do not indicate the existence of multiple thermal niches that consistently mirror colour polymorphism. We suggest that while a relationship between colour morph and thermal niche selection appears to exist it is neither simple nor consistent.     

Behavioural fitness component effects of the alba polymorphism of Colias (Lepidoptera, Pieridae): resource and time budget analysis

1. Alba, a white wing colour morph of butterflies of the genus Colias , makes fitness-related changes at several levels of phenotypic organization: physiology, development and behaviour. Two sympatric species of Colias are studied, which differ greatly in their frequency of alba vs its sister yellow/orange morph. How resource and time constraints on Colias interact with the morphs' different patterns of pupal resource allocation to alter the balance of the morphs' fitness components in the two species is discussed.
2. These species, C. alexandra and C. scudderi , differ in melanin-based solar energy absorption, in larval dietary richness and in local adult nectar resources. The two female morphs determine alternate thermal balance, internal resource allocation and behavioural effects in each species, thus changing the morphs' time budgets and fitness-component impacts between the species. In particular, female egg output differences between the morphs appears to reverse between species: alba fecundity is greater than yellow fecundity in C. scudderi , but alba is less than yellow in C. alexandra .
3. These differences are consistent with the large observed differences in alba frequency between the species. Some important questions about the selective regime maintaining a polymorphism here, rather than an alternation of monomorphisms, remain.     

Dorsal pattern polymorphism in female Iberian wall lizards: differences in morphology,dorsal coloration,immune response,and reproductive investment

Sex‐specific colour polymorphisms have been extensively documented in many different taxa. When polymorphism in colour pattern is restricted to females, the condition is known as female‐limited pattern polymorphism (FPP), which has been less commonly addressed in vertebrates. FPP is present in several lizard species, although most research on lizards has focused on carotenoid‐ and pteridine‐based coloration and not on melanin‐based polymorphisms. In the present study, we focus on Iberian wall lizards, Podarcis hispanicus, where two female melanin‐based dorsal patterns can be clearly distinguished: striped and reticulated‐blotched. We indirectly tested the hypothesis that selection acts differentially among P. hispanicus female morphs to create alternative morph‐specific phenotypic optima at different levels by investigating whether morphs differ in fitness proxies. We specifically examined whether the two female dorsal pattern morphs differed in adult morphology, dorsal coloration, immune response, reproductive investment, and growth. We did not find a relationship between melanin‐based coloration and hatchling growth and immune response, despite a correlation between these traits possibly being expected as a result of pleiotropy in the melanocortin system. However, our results show that female dorsal morphs in P. hispanicus differ in terms of adult morphology, dorsal coloration, and reproductive investment. Reticulated‐blotched P. hispanicus females had deeper heads and longer femora, less melanin, and more brownish coloration, and also had larger and heavier hatchlings than striped females.     

Environmentally induced changes in carotenoid-based coloration of female lizards: a comment on Vercken et al

Colouration may either reflect a discrete polymorphism potentially related to life-history strategies, a continuous signal related to individual quality or a combination of both. Recently, Vercken et al. [J. Evol. Biol. (2007) 221] proposed three discrete ventral colour morphs in female common lizards, Lacerta vivipara, and suggested that they reflect alternative reproductive strategies. Here, we provide a quantitative assessment of the phenotypic distribution and determinants of the proposed colour polymorphism. Based on reflectance spectra, we found no evidence for three distinct visual colour classes, but observed continuous variation in colour from pale yellow to orange. Based on a 2-year experiment, we also provide evidence for reversible colour plasticity in response to a manipulation of the adult population sex ratio; yet, a significant portion of the colour variation was invariant throughout an adult female's life. Our results are thus in agreement with continuous colour variation in adults determined by environmental factors and potentially also by genetic factors.     

Male sexual polymorphism, alternative reproductive tactics, and androgens in combtooth blennies (pisces: blenniidae)

In species in which intense intermale competition for the access to females is present males of lower competitive ability may adopt alternative reproductive tactics (ART) to get access to mates. These ART translate in many cases into male sexual polymorphism, with individuals following distinctly different tactics. Usually two alternative male morphs can be recognized in species with ART: (1) bourgeois males that compete for access to mates invest in typically male behaviors, such as building elaborated nests or displaying ornaments; and (2) parasitic males that take advantage of the success of the bourgeois males in attracting females and attempt "sneaker" fertilizations (e.g., sneaker and satellite males). In combtooth blennies (Blenniidae) the co-occurrence of ART and male sexual polymorphism has been described for two temperate species: the peacock blenny, Salaria pavo, and the Azorean rock-pool blenny, Parablennius sanguinolentus parvicornis. Interestingly, while in the peacock blenny the alternative male morph adopts a sneaker tactic, in the rock-pool blenny parasitic males act as satellites to nest-holder males. Thus, this variation in the ART expressed in these two closely related species allows for a comparative study of the proximate and ultimate factors affecting the expression of the two ART. In this article we summarize the available information on androgen levels in bourgeois and parasitic males of natural populations of the two species and of recent studies on the effect of exogenous administration of androgens on tactic switching in parasitic males of the two species. The information is discussed within the frame of the relative plasticity hypothesis, which predicts that plastic alternative morphs should show differences in hormone levels and that the administration of sex steroids should be effective in promoting the switch from the parasitic to bourgeois tactic. The evidence is only partly consistent with this hypothesis. Alternatively, a social transduction hypothesis that better fits the available data on androgens and ART in teleost is proposed. It states that the observed differences in androgen levels between alternative morphs should not be interpreted as an organization vs activation effect of steroids, but rather as the limited vs lifelong responsiveness of the neuroendocrine axis to social regulation.