Reaction norms and the genetic basis of phenotypic plasticity in the wing pattern of the butterfly Bicyclus anynana

The genetic basis of the dry-wet season polyphenism of wing pattern in response to temperature shown by Bicyclus anynana was studied, using a split-family design over four temperatures. Reaction norms crossed, but were only linear in the three highest temperatures, and only when larval development time was used as the environmental axis. Significant full-sib additive variances (V_A) and heritabilities (h²) for plasticity were found using slopes of reaction norms in a bootstrap procedure. Heritabilities were lower in intermediate temperatures, mainly due to differences in the residual variances (V_R). There was no clear trend in V_A across temperatures, contrary to the expectation that V_A would have been depleted by natural selection at the extreme temperatures and not depleted at the intermediate temperatures which occur less frequently in the field. Unpredictability in the onset of the following season at intermediate temperatures might lead to selection for diverse flresponses resulting in relatively high V_Rs. Theoretical models linking reaction norms to genetic parameters in separate environments were difficult to apply in this study, particularly because they are based on the assumption that V_Rs are constant. However the reaction norm approach combined with quantitative genetics provided a valuable insight into the evolution of the observed polyphenism.     

Natal philopatry in passerine birds: genetic or ecological influences?

The degree of natal philopatry (the likelihood that individualsbreed at or near their place of origin) can influence the extentof inbreeding in animal populations. Passerine birds have beencited as typically showing high natal philopatry, and natalphilopatry has been proposed as an adaptation to promote optimalinbreeding. A review of published and unpublished studies ofpasserines showed that natal philopatry was typically low, somaintaining a high level of inbreeding appears relatively unimportantfor such birds. Rather, natal philopatry appeared to be morestrongly influenced by ecological factors. Migratory passerineexhibited low natal philopatry compared to resident passerines,as predicted if dispersal costs for young birds are an importantdeterminant of natal philopatry. The erroneous view that natalphilopatry for passerines is generally high has resulted froma reporting bias toward resident species that have sufficientnatal philopatry to study. Natal philopatry was found to beevolutionarily labile; populations of the same species and pairsof closely related species that differed in their degree ofisolation differed considerably in their degree of philopatry.Future studies of natal philopatry should consider both theecological factors that could affect dispersal costs and thereporting biases that influence which data on philopatry tendto be reported.     

The fecundity patterns of S and L type rotifers of Brachionus plicatilis

Fecundity patterns of S and L type rotifers Brachionus plicatilis, which were previously found to have distinct growth ability, were analyzed using data of age-specific fecundity. The data were obtained by individual cultures of S and L type strains at 17, 24 and 34 °C. The pattern was analyzed by using normal probability functions. When the age was transformed into logarithmic value, the S and L types had an identical pattern of fecundity at every temperature. This fact indicates that the difference of the growth response to the temperature between S and L type strains stemmed only from the differences in net reproduction rate, not from the pattern.     

Zoogeography and life cycle patterns of Mediterranean hydromedusae (Gnidaria)

The distribution of the 346 hydromedusan species hitherto recorded from the Mediterranean is considered, dividing the species into zoogeographical groups. The consequences for dispersal due to possession or lack of a medusa stage in the life cycle are discussed, and related to actual known distributions. There is contradictory evidence for an influence of life cycle patterns on species distribution. The Mediterranean hydromedusan fauna is composed of 19.5% endemic species. Their origin is debatable. The majority of the remaining Mediterranean species is present in the Atlantic, with various world distributions, and could have entered the Mediterranean from Gibraltar after the Messinian crisis. Only 8.0% of the fauna is classified as Indo-Pacific, the species being mainly restricted to the eastern basin, some of which have presumably migrated from the Red Sea via the Suez Canal, being then classifiable as Lessepsian migrants. The importance of historical and climatic factors in determining the composition of the Mediterranean fauna of hydromedusae is discussed.     

Spring dispersal ofSitona lineatus: The use of aggregation pheromone traps for monitoring

The spring dispersal ofSitona lineatus L. (Coleoptera; Curculionidae) was investigated on a Danish farm.S. lineatus dispersed by flight in the early spring on sunny, calm days with temperatures above ca. 15°C. Two thirds of the population ofS. lineatus dispersed from perennial leguminous crops (clover and lucerne) in the first period of flight activity. The next dispersal did not occur until one month later despite several intermediate flight activity periods. The first period of dispersal occurred before the germination of the spring sown summer host crop,Vicia faba L. The field bean crop was infested in three later invasions during a period of more than three weeks. The aggregation pheromone, 4-methyl-3,5-heptanedione, had a significant effect on captures of both males and females in cone traps placed on the ground. There was no effect of the pheromone on captures in yellow sticky traps placed 1.5 m above ground. The pheromone effect is discussed in relation to behavioural observations. Both types of traps may be used in a survey system for monitoring spring dispersal ofS. lineatus and optimal timing of insecticide spraying. However, the pheromone cone traps were highly specific whereas all kinds of flying insects were caught in the yellow sticky traps, thus making the latter traps less suitable for monitoring.     

HOMOGENEITY OF THE GENETIC VARIANCE-COVARIANCE MATRIX FOR ANTIPREDATOR TRAITS IN TWO NATURAL POPULATIONS OF THE GARTER SNAKE THAMNOPHIS ORDINOIDES

Quantitative genetic models of evolution rely on the genetic variance-covariance matrix to predict the phenotypic response to selection. Both prospective and retrospective studies of phenotypic evolution across generations rely on assumptions about the constancy of patterns of genetic covariance through time. In the absence of robust theoretical predictions about the stability of genetic covariances, this assumption must be tested with empirical comparisons of genetic parameters among populations and species. Genetic variance-covariance matrices were estimated for a suite of antipredator traits in two populations of the northwestern garter snake, Thamnophis ordinoides. The characters studied include color pattern and antipredator behaviors that interact to facilitate escape from predators. Significant heritabilities for all traits were detected in both populations. Genetic correlations and covariances were found among behaviors in both populations and between color pattern and behavior in one of the populations. Phenotypic means differed among populations, but pairwise comparisons revealed no heterogeneity of genetic parameters between the populations. The structure of the genetic variance-covariance matrix has apparently not changed significantly during the divergence of these two populations.     

CONSERVATION OF MOLECULAR PREPATTERNS DURING THE EVOLUTION OF CUTICLE MORPHOLOGY IN DROSOPHILA LARVAE

We are using patterns of cuticle specialization in Drosophila larvae as models to investigate the molecular, genetic, and developmental bases of morphological evolution. Members of the virilis species group differ markedly from one another in the distribution of hairs on the dorsal surface of first instar larvae. In particular, characteristic bands of hairs cover about 20% of each trunk segment in some species but about 70% in others. These major types do not correlate with recently proposed phylogenetic relationships, suggesting that similar phenotypes have arisen independently in different lineages. The patterns of expression of several genes that control or reflect intrasegmental patterning are indistinguishable in species with very different cuticle morphologies. We conclude that, in this case, morphology probably has evolved via altered response to a conserved molecular prepattern.     

Storage-protein variation in wild emmer (Triticum turgidum ssp.dicoccoides) from Jordan and Turkey.

Genetic diversity in the seed storage-proteins encoded at theGlu-A1,Glu-B1 andGli-B1/Glu-B3 loci was studied electrophoretically in 315 individuals belonging to nine populations ofT. dicoccoides from Jordan and three from Turkey. The inter- and intra-population distribution of seed storage-protein alleles at the considered loci and its link with geographical factors were investigated. Population differentiation in seed storage-proteins was in some cases very high with very weak correlations with geographic distance. Greater gene differentiation was found within and between populations which were geographically very close in Jordan than between those from Jordan and Turkey. However the distribution of alleles appeared to be non random. Samples collected from populations at locations over 900 m above sea level were less polymorphic than those collected at lower altitudes (500–700 m), whereas the relative genetic differentiation between populations was greater between those collected at higher altitudes. Seed storage-protein differentiation was significantly correlated with the altitude of the collecting sites. Although it is difficult to point out the selective pressure of altitude per se, altitude can reflect an integration of several environmental parameters. The possible adaptive value of seed storage-proteins is discussed.     

Site fidelity in predictable and unpredictable habitats

Summary Site fidelity, the tendency to return to a previously occupied location, has been observed in numerous species belonging to at least three phyla. In this paper I develop a general model using dynamic programming to investigate conditions under which fidelity to a previously occupied territory will be advantageous. The results predict that site fidelity should be inversely related to heterogeneity in territory quality and the animal's lifespan and positively related to the cost of changing territories, age and probability of mortality in the habitat. The predictability of reproductive outcome (defined as the probability that next period's outcome will be the same as this period's outcome) also affects site fidelity. In predictable habitats, changing territories may be favoured after a bad previous outcome. In contrast, settlement should be independent of the previous outcome in unpredictable habitats. Individuals should also be site-faithful in unpredictable habitats, as long as the mean territory quality is equal among available territories. I also investigate the success of two potential decision rules (always stay and win-stay: lose-switch) relative to the optimal settlement strategy. The results show that these rules may perform as well as the optimal strategy under certain conditions. The always stay strategy does well in unpredictable habitats, when the mean quality within a territory is equal among territories. In contrast, the win-stay: lose-switch strategy performs best in predictable habitats.