Is Size of Fecal Pellets a Reliable Indicator of Species of Leporids in the Southern Rocky Mountains?

Abstract: In the southern Rocky Mountains, USA, snowshoe hares (Lepus americanus) and mountain cottontails (Sylvilagus nuttallii) are syntopic. Previous researchers used size of fecal pellets to identify leporid species in the Southern Rockies, a common criterion for identifying species of cervids. We measured 655 fecal pellets from 10 mountain cottontails and 2,374 fecal pellets from 23 snowshoe hares. We found no relationship between the body weight of mountain cottontails and the size of their fecal pellets (r = 0.04, F = 0.01, P = 0.91) but found one for snowshoe hares (r = 0.48, F = 9.3, P = 0.005). Although the 2 species differed in the size of their fecal pellets, the difference between means (1.2 mm) was sufficiently small to require measuring individual pellets and is only applicable to individuals of adult size. Although fecal pellet counts may be used to estimate presence and relative abundance of snowshoe hares in the absence of syntopic leporids, where multiple species of leporids are syntopic this method may yield misleading results.     

Thermoregulation and activity patterns of two syntopic cicadas,Tibicen chiricahua and T. duryi (Homoptera: Cicadidae), in central New Mexico

Summary Tibicen chiricahua and T. duryi are cicada species that are active as adults early each summer in central New Mexico, and are often syntopic in pinyon-juniper woodlands. Both species regulate thoracic temperature (T_th) within fairly narrow limits by utilizing behavioral mechanisms and evaporative cooling. However, syntopic populations of these two species were found to regulate at different T_th despite having synchronous annual and daily activity periods; overall mean T_th of T. chiricahua was 3.1°C higher than it was for T. duryi. Interspecific differences in evaporative cooling abilities and rates of passive heat exchange could not account for this difference in T_th. Part of the difference in T_th resulted from the fact that individuals of the two species were active in thermally distinct microhabitats. Within each species, mean T_th varied among behavior categories, and differences in how the two species allocated their time between activities also contributed to the interspecific difference in T_th. Though T. duryi is restricted to pinyon-juniper habitats such as the one in this study, T. chiricahua is also found in warmer habitats. The difference in T_th in the syntopic populations probably reflects interspecific differences in thermal preferences and thermal optima that are adaptive over their respective habitat ranges. The degree of dependence of T_th on ambient temperature (T_am) varied between activities within both species, with the least dependence exhibited during singing. Singing involves intense activity of tymbal muscles, which apparently can only function effectively over a relatively narrow range of temperature.     

Effects of artificial stabilizing selection on Drosophila populations subjected to directional selection for another trait

Stabilizing selection for a set of morphometric wing traits was combined with directional selection for the increased expression of radius incompletus (ri) mutation of Drosophila melanogaster. Three experimental regimes were used: directional and stabilizing selection (stabilized lines); directional selection (unstabilized lines); no selection (controls). Response to selection for ri expression was similar in all selected lines but variation of this character was higher in the unstabilized lines compared to the stabilized ones. The competitive indices measured after termination of selection did not significantly differ under different treatments while fluctuating asymmetry was significantly lower in stabilized than in unstabilized lines. The possible causes of these differences are discussed.     

NATURAL SELECTION ON FLORAL TRAITS IN TWO SPECIES OF LOBELIA WITH DIFFERENT POLLINATORS

Using both multivariate and univariate regression techniques, I measured selection acting through female reproductive success in two hermaphroditic species with precise pollen placement but different pollinators: hummingbird-pollinated Lobelia cardinalis and bumblebee-pollinated L. siphilitica. Six traits were analyzed in two populations of L. cardinalis and one population of L. siphilitica: flower number, mean number of flowers open per day, inflorescence height, number of days in flower, median-flower date and nectar-stigma distance. In another study it was found that female reproductive success in one population of L. cardinalis was much less pollen limited than in the other two populations, and it was therefore expected that selection of female reproductive traits in this population would be weaker. In the univariate analyses correlations caused nearly all traits to have significant directional selection coefficients. However, in the multivariate analyses no traits in L. siphilitica experienced directional or quadratic selection. Selection acted differently in the two L. cardinalis populations. The less pollen-limited population experienced positive directional selection on flower number and median-flower date, while in the other L. cardinalis population there was positive directional selection on flower number and nectar-stigma distance and both positive directional and positive quadratic selection on height. The functional significance of floral traits in these two species and the probable effect of increased sample sizes are discussed.     

VARIABLE SELECTION ON EUROSTA'S GALL SIZE,I: THE EXTENT AND NATURE OF VARIATION IN PHENOTYPIC SELECTION

Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in phenotypic selection. The intensity of selection imposed by parasitoids and predators on gallmaking larvae, for gall size, was measured across 16 populations over the course of 4 generations, for a total of 64 population-generations. Directional selection was quantified by i, the selection intensity, and variance selection by j‘, a measure of the intensity of selection on phenotypic variance. Size-dependent attack by parasitoids caused upward directional selection (mean i_p = 0.42; SE = 0.023), while size-dependent bird attack favored larvae that induced smaller galls (mean i_b = -0.07; SE = 0.013. The mean net directional selection intensity was 0.35 (SE = 0.030), which indicates that insects inducing larger galls are generally favored by selection. The opposing patterns of size-dependent attack resulted in stabilizing selection in half the population generations, with an overall average. j‘ of -0.11 (SE = 0.078). The magnitude of directional selection was strongly influenced by the population mean gall size and weakly by the optimal gall size. The intensity of variance selection was strongly influenced by the shape of the fitness function, with sigmoidal and Gaussian-like shapes causing greater depletion of phenotypic variance.     

VARIABLE SELECTION ON EUROSTA'S GALL SIZE. II. A PATH ANALYSIS OF THE ECOLOGICAL FACTORS BEHIND SELECTION

We examined phenotypic selection exerted by natural enemies on the gall-making fly Eurosta solidaginis in an extensive field study of 16 populations, spanning four generations. Gall-makers that induce small galls are vulnerable to the attack of Eurytoma gigantea. This imposes upward directional selection on gall size. Insectivorous birds, predominantly the downy woodpecker, are more likely to attack larvae that induce large galls than small ones, and this imposes downward directional selection. We used path analysis to explore the relative contributions of these natural enemies to the net directional selection on gall size. The path models further examined several ecological factors that influence selection intensity through their effects on parasitoid and bird attack rates. Net directional selection varied more strongly with E. gigantea attack than bird attack. Competitive interactions among birds and the three parasitoid species, including E. gigantea, were evidenced by low winter bird attack rates in fields where a high proportion of galls contained the overwintering parasitoids. Eurytoma gigantea attack was heavier in fields where mean gall size was small and bird attack heavier in fields where mean gall size was large. Neither birds nor E. gigantea showed simple density-dependent attack. Data suggested a form of frequency-dependent attack by birds but not by E. gigantea.     

Apparent directional selection by biased pleiotropic mutation

Pleiotropic effects of deleterious mutations are considered to be among the factors responsible for genetic constraints on evolution by long-term directional selection acting on a quantitative trait. If pleiotropic phenotypic effects are biased in a particular direction, mutations generate apparent directional selection, which refers to the covariance between fitness and the trait owing to a linear association between the number of mutations possessed by individuals and the genotypic values of the trait. The present analysis has shown how the equilibrium mean value of the trait is determined by a balance between directional selection and biased pleiotropic mutations. Assuming that genes act additively both on the trait and on fitness, the total variance-standardized directional selection gradient was decomposed into apparent and true components. Experimental data on mutation bias from the bristle traits of Drosophila and life history traits of Daphnia suggest that apparent selection explains a small but significant fraction of directional selection pressure that is observed in nature; the data suggest that changes induced in a trait by biased pleiotropic mutation (i.e., by apparent directional selection) are easily compensated for by (true) directional selection.     

Temporal variation in diets and trophic partitioning by coexisting lizards (Ctenotus: Scincidae) in central Australia

Summary The diets of five syntopic species of Ctenotus were examined over a two-year period on a 60 ha spinifex grassland site in central Australia. The aims of the study were to test predictions that termites were an important part of the food web for syntopic Ctenotus in spinifex grasslands, and to examine seasonal changes in prey use and dietary overlap between the species. Environmental conditions during the first season of the study were dry resulting in generally low invertebrate abundance. In contrast the second season was relatively moist and overall invertebrate abundance was higher than in the first season. Diets of five species of Ctenotus contained a range of terrestrial prey although one species (C. pantherinus) was relatively termite-specialized at all times. Dietary overlap at the ordinal level between the species was generally higher during dry periods when prey abundance was low, and higher for species-pairs that were similar in body size. During the driest period of the study most species of Ctenotus ate a high proportion of termite prey which accounted for the high dietary overlap. However, each species of Ctenotus consumed different genera or foraging guilds of termites. The results suggest that most of these lizards were opportunistic in their selection of prey but that during dry periods when prey are scarce, termites may play a significant role in supporting a high -diversity of Ctenotus.     

Directional selection in the evolution of elongated upper canines in clouded leopards and sabre‐toothed cats

Extremely developed or specialized traits such as the elongated upper canines of extinct sabre‐toothed cats are often not analogous to those of any extant species, which limits our understanding of their evolutionary cause. However, an extant species may have undergone directional selection for a similar extreme phenotype. Among living felids, the clouded leopard, Neofelis nebulosa, has exceptionally long upper canines for its body size. We hypothesized that directional selection generated the elongated upper canines of clouded leopards in a manner similar to the process in extinct sabre‐toothed cats. To test this, we developed an approach that compared the effect of directional selection among lineages in a phylogeny using a simulation of trait evolution and approximate Bayesian computation. This approach was applied to analyse the evolution of upper canine length in the Felidae phylogeny. Our analyses consistently showed directional selection favouring longer upper canines in the clouded leopard lineage and a lineage leading to the sabre‐toothed cat with the longest upper canines, Smilodon. Most of our analyses detected an effect of directional selection for longer upper canines in the lineage leading to another sabre‐toothed cat, Homotherium, although this selection may have occurred exclusively in the primitive species. In all the analyses, the clouded leopard and Smilodon lineages showed comparable directional selection. This implies that clouded leopards share a selection advantage with sabre‐toothed cats in having elongated upper canines.     

THE EVOLUTION OF RESISTANCE TO HERBIVORY IN IPOMOEA PURPUREA. I. ATTEMPTS TO DETECT SELECTION

In this study, we looked for evidence of directional or stabilizing/disruptive selection on plant size and on the level of damage (resistance) caused by four types of herbivores in the annual morning glory Ipomoea purpurea. Selection was estimated by standard phenotypic regression analysis and by regression on breeding values. The phenotypic regression analysis revealed directional selection for all five characters (i.e., plant size and resistance to four types of herbivores) and indicated that plant size and resistance to corn-earworm damage were subject to stabilizing selection. By contrast, the analysis using breeding values revealed directional selection only for plant size and resistance to corn earworms, while none of the characters examined indicated stabilizing or disruptive selection. These results suggest that intermediate levels of damage in I. purpurea are, in general, not maintained by stabilizing selection. Rather, they may reflect either 1) a transient state that exists while directional selection pushes the population toward complete resistance (or, in one case, total absence of resistance) or 2) the evolution of susceptibility to damage by genetic drift.     

Evolutionary genetics of Drosophila ananassae. I. Effect of selection on body size and inversion frequencies

Adaptive importance of inversion polymorphism has been discussed in Drosophila species at several levels but no study has been carried out demonstrating the individual and combined effects of polymorphic inversions on the fitness of flies through bi‐directional selection. Therefore, artificial bi‐directional selection for thorax length in Drosophila ananassae was carried out for 10 generations. Both, Tukey test for selection difference and regression coefficients of offspring on mid‐parent are highly significant. The realized heritability (h²) in males of both high and low selection lines is more or less similar but is more pronounced in low line females, which suggests the asymmetrical response. This asymmetry in selection is discussed in the light of evidence provided by the study of chromosome inversion frequencies in different selection lines at different generations of selection. Interestingly, chromosome inversion frequency changes towards homozygosity for different gene arrangements in different selection lines. Tests of correlations at G₆ and G₁₀ among different gene arrangements as well as with mean thorax length suggest that 2L‐ST gene arrangement is negatively correlated, while 3L‐ST gene arrangement is positively correlated with thorax length. Furthermore, the present study shows the significant effects of 3L‐ST and 2L + 3L (positive correlation) on thorax length, while 3R‐ST and 2L + 3R show significant effect (negative correlation) on thorax length, which was not evident in the previous study. Present results also suggest how polymorphic inversions and their combinations affect the body size differently in different selection lines. These results suggest that thorax length in D. ananassae is under polygenic control and inversion polymorphism plays crucial role in maintaining body size by modifying genotypic frequency under various selection pressures.     

Viability selection on prey morphology by a generalist predator

Prey use their locomotory capacity to escape predators, and there should thus be strong viability selection on locomotory morphology of prey. We compared feather morphology of wood pigeons Columba palumbus killed by goshawks Accipiter gentilis with that of survivors to quantify directional and quadratic selection on primary and rectrix feathers. The goshawk is mainly a predator attacking by surprise, leaving wood pigeons with an ability to accelerate fast at a selective advantage. There was directional selection for light primary feathers with a narrow calamus. In addition, there was directional selection for increased area of rectrices. These patterns of natural selection were confirmed in multivariate analyses of selection that showed selection for light primary feathers with a large area and narrow calamus and for a large area of rectrix feathers. These results provide evidence of selection on different aspects of feather morphology directly related to flight performance and thus escape ability from predators.     

VIABILITY SELECTION ON SEASONALLY POLYPHENIC TRAITS: WING MELANIN PATTERN IN WESTERN WHITE BUTTERFLIES

Wing melanin pattern varies seasonally among generations in many populations of the butterfly Pontia occidentalis, leading to distinctly different wing phenotypes during spring and summer generations. Estimates of directional selection on wing pattern can therefore quantify the imperfection of this phenotypically plastic (polyphenic) response in generating “optimal” phenotypes for each seasonal generation. Mark-release-recapture (MRR) studies were used to estimate directional selection on six wing traits in a natural population of P. occidentalis during both spring and summer weather conditions. Estimated survival and recapture probabilities varied substantially among the four MRR studies. When differences between males and females were detected, the survival and recapture probabilities were higher for males than for females. Estimated selection coefficients suggested that the direction of selection on one wing trait important for thermoregulation, melanin on the base of the dorsal hindwings (trait hb), fluctuated seasonally; there was evidence of directional selection for increased hb in the spring studies and for decreased hb in the summer studies. Such fluctuating seasonal selection on hb implies that the seasonal polyphenic response may not be sufficient to eliminate selection on this trait; the slope of the reaction-norm mapping hb onto seasonal environmental cues is too shallow, resulting in further selection on the reaction norm. Adaptive evolution of the reaction norm may be constrained by phenotypic and genetic correlations with other wing traits that experience different patterns of selection and by variable weather conditions within seasons and among years.     

Survival selection on escape performance and its underlying phenotypic traits: a case of many‐to‐one mapping

Selection often operates not directly on phenotypic traits but on performance which is important as several traits may contribute to a single performance measure (many‐to‐one mapping). Although largely ignored in the context of selection, this asks for studies that link all relevant phenotypes with performance and fitness. In an enclosure experiment, we studied links between phenotypic traits, swimming performance and survival in two Enallagma damselflies. Predatory dragonflies imposed survival selection for increased swimming propensity and speed only in E. annexum; probably E. aspersum was buffered by the former species’ presence. Accordingly, more circular caudal lamellae, structures involved in generating thrust while swimming, were selected for only in E. annexum. Other phenotypic traits that contributed to swimming speed were apparently not under selection, probably because of many‐to‐one mapping (functional redundancy). Our results indicate that not only the phenotypic distributions of syntopic prey organisms but also many‐to‐one mapping should be considered when documenting phenotype–performance–fitness relationships.     

Evidence for complex selection on four‐fold degenerate sites in Drosophila melanogaster

We considered genome‐wide four‐fold degenerate sites from an African Drosophila melanogaster population and compared them to short introns. To include divergence and to polarize the data, we used its close relatives Drosophila simulans, Drosophila sechellia, Drosophila erecta and Drosophila yakuba as outgroups. In D. melanogaster, the GC content at four‐fold degenerate sites is higher than in short introns; compared to its relatives, more AT than GC is fixed. The former has been explained by codon usage bias (CUB) favouring GC; the latter by decreased intensity of directional selection or by increased mutation bias towards AT. With a biallelic equilibrium model, evidence for directional selection comes mostly from the GC‐rich ancestral base composition. Together with a slight mutation bias, it leads to an asymmetry of the unpolarized allele frequency spectrum, from which directional selection is inferred. Using a quasi‐equilibrium model and polarized spectra, however, only purifying and no directional selection is detected. Furthermore, polarized spectra are proportional to those of the presumably unselected short introns. As we have no evidence for a decrease in effective population size, relaxed CUB must be due to a reduction in the selection coefficient. Going beyond the biallelic model and considering all four bases, signs of directional selection are stronger. In contrast to short introns, complementary bases show strand specificity and allele frequency spectra depend on mutation directions. Hence, the traditional biallelic model to describe the evolution of four‐fold degenerate sites should be replaced by more complex models assuming only quasi‐equilibrium and accounting for all four bases.     

Molecular changes in the maize composite EPS12 during selection for resistance to pink stem borer

The pink stem borer (Sesamia nonagrioides Lefèvbre) is the most important pest of maize (Zea mays L.) throughout the Mediterranean area. The maize composite EPS12 has been chosen as the base population for a breeding program based on its resistance to pink stem borer, with the main selection criterion being resistance to stem tunneling. Yield was taken as a secondary selection criterion to avoid any unwanted negatively correlated response on this character. The aims of investigation were: (1) to monitor the effects of selection for resistance to pink stem borer on allele frequency at 70 simple sequence repeat (SSR) markers and their impact on the genetic structure of EPS12 and (2) to identify loci at which allelic frequencies changed significantly due to directional selection. Genetic diversity was reduced during the selection process (as expected since random genetic drift as well as selection could reduce genetic variability), but not significantly so. Although the loss of genetic variation was generally consistent with that expected in a model in which random genetic drift acts alone on neutral alleles, the changes observed in the frequency of five alleles were significantly greater than expected. Further, the linear trend of the departure from the random genetic drift model was significant for some allelic versions of two SSR markers, umc1329 and phi076; directional selection was therefore acting on these loci. The significant effect of directional selection on those markers suggests the presence of quantitative trait loci (QTLs) for tunnel length and/or for yield under artificial infestation with Sesamia nonagrioides on the long arm of chromosome 4.     

Interspecific Aggression between Lizard Competitors,Anolis cooki and Anolis cristatellus

Aggressive encounters were staged between two species of Puerto Rican lizards (Anolis cooki and Anolis cristatellus) which share the same microhabitat (syntopic). The intensity of these interspecific matches was as great as their respective conspecific matches. When the two species interacted with either “look alike” congeners (A. cooki with A. monensis and A. cristatellus with A. gundlachi) or with the quite different appearing A. evermanni, aggressive intensity was only 1/6 that of the cooki-cristatellus encounters. It seems that A. cooki and A. cristatellus recognize each other as competitors; it was improbable that this interspecific aggression was caused by the two species misidentifying each other as conspecifics. Because A. cristatellus eventually dominated A. cooki during staged encounters, it is predicted A. cristatellus should ecologically displace A. cooki in their syntopic zones of contact.     

Pollinator‐mediated selection in a specialized hummingbird–Heliconia system in the Eastern Caribbean

Phenotypic matches between plants and their pollinators often are interpreted as examples of reciprocal selection and adaptation. For the two co‐occurring plant species, Heliconia bihai and H. caribaea in the Eastern Caribbean, we evaluated for five populations over 2 years the strength and direction of natural selection on corolla length and number of bracts per inflorescence. These plant traits correspond closely to the bill lengths and body masses of their primary pollinators, female or male purple‐throated carib hummingbirds (Eulampis jugularis). In H. bihai, directional selection for longer corollas was always significant with the exception of one population in 1 year, whereas selection on bract numbers was rare and found only in one population in 1 year. In contrast, significant directional selection for more bracts per inflorescence occurred in all three populations of the yellow morph and in two populations of the red morph of H. caribaea, whereas significant directional selection on corolla length occurred in only one population of the red morph and one population of the yellow morph. Selection for longer corollas in H. bihai may result from better mechanical fit, and hence pollination, by the long bills of female E. jugularis, their sole pollinator. In contrast, competition between males of E. jugularis for territories may drive selection for more bracts in H. caribaea. Competitive exclusion of female E. jugularis by territorial males also implicates pollinator competition as a possible ecological mechanism for trait diversification in these plants.     

QUANTITATIVE GENETICS OF BRYOZOAN PHENOTYPIC EVOLUTION. II. ANALYSIS OF SELECTION AND RANDOM CHANGE IN FOSSIL SPECIES USING RECONSTRUCTED GENETIC PARAMETERS

The roles of natural selection and random genetic change in the punctuated phenotypic evolution of eight Miocene-Pliocene tropical American species of the cheilostome bryozoan Metrarabdotos are analyzed by quantitative genetic methods. Trait heritabilities and genetic covariances reconstructed by partitioning within- and among-colony phenotypic variance are similar to those previously obtained for living species of the cheilostome Stylopoma using breeding data. The hypothesis that differences in skeletal morphology between species of Metrarabdotos are entirely due to mutation and genetic drift cannot be rejected for reasonable rates of mutation maintained for periods brief enough to account for the geologically abrupt appearances of these species in the fossil record. Except for one pair of species, separated by the largest morphologic distance, directional selection acting alone would require unrealistically high rates of selective mortality to be maintained for these periods. Thus, directional selection is not strongly implicated in the divergence of Metrarabdotos species. Within species, rates of net phenotypic change are slow enough to require stabilizing selection, but mask large, relatively rapid fluctuations, all of which, however, can be attributed to chance departures from the mean phenotype by mutation and genetic drift, rather than to tracking environmental fluctuation by directional selection. The results are consistent with genetic models involving shifts between multiple adaptive peaks on which phenotypes remain more or less static through long-term stabilizing selection. Regardless of the degree to which directional selection may be involved in peak shifts, phenotypic differentiation is thus related to processes different than the pervasive stabilizing selection acting within species.     

Habitat preferences of tree pipit ( Anthus trivialis) and meadow pipit ( A. pratensis) at sympatric and allopatric localities

Habitat preferences of the tree pipit (Anthus trivialis) and the meadow pipit (A. pratensis; Passeriformes: Motacillidae) were observed during the years 1998–1999 at three localities in the Czech Republic; two with one pipit species only, and a third with both species present. We investigated one of the possible mechanisms allowing syntopic coexistence—different habitat selection. We characterised territories of each pipit pair by the habitats present in the territory (defined by dominant plant composition) and by quantitative parameters (territory size, height and density of the vegetation, number of look-outs of different height categories, and proportion of wet ground). Tree pipits preferred significantly higher vegetation of lower density than meadow pipits, and there was generally a higher number of high look-outs in their territories. However, in some of the preferred territories at the allopatric locality of the tree pipit, steep hill slopes could well substitute for higher look-outs, which were almost absent. The two pipit species at the sympatric locality occupied very different habitats, which was also reflected in quantitative parameters of their territories. The available data of pipit habitat at different European localities show that the two species can occupy a much wider range of habitats. The habitat separation in sympatry might therefore be one of the mechanisms allowing syntopic coexistence of both species.Communicated by F. Bairlein