Ethological Isolation,Sexual Behavior and Pheromones in the Fasciatus Species Group of the Lizard Genus Eumeces

Ethological isolation was found among North American members of the fasciatus species group of Eumeces. Ethological isolation was investigated by staging a series of interspecific and intraspecific heterosexual encounters. No male E. laticeps or E. fasciatus courted heterospecific females. In both species, males courted and copulated with conspecific females in a significantly higher frequency of trials than with heterospecific females. However, male E. inexpectatus courted females of all three species, courting conspecific females and female E. laticeps at similar frequencies, but female E. fasciatus at a significantly lower frequency. No females of any of the three species were sexually receptive to heterospecific males, but forced copulation occurred in two of nine courtships of female E. fasciatus by male E. inexpectatus. Thus, ethological isolation in the fasciatus group appears to be complete with the possible exception of occasional forced copulation between male E. inexpectatus and female E. fasciatus. Preliminary evidence on the role of chemical stimuli in maintaining ethological isolation was obtained from experiments involving interspecific transfers of female odors. Male E. inexpectatus courted female E. fasciatus labelled with the odor of female E. inexpectatus in a significantly greater proportion of trials than they courted such females lacking the conspecific female odor. In a similar experiment, male E. fasciatus did not court female E. inexpectatus even if the females bore odors of female fasciatus.     

Phylogenesis / biotope interactions among formicidae

The development of interspecific recognition and the expression of behavioral plasticity as a function of phyletic distance and the natural environment in which the ants live were investigated.An experimental model involving artificial mixed societies was used in this study. These mixed societies were produced by combining ants from two out of the 11 investigated species. The possibilities thus ranged from situations in which phylogenetically similar ants that live in the same biotype were combined, to those in which the species differ significantly in terms both of phyletic distance and of biotope.The interspecific groups were established in a neutral environment with adult ants less than 24 hours old. The results concerned agonistic and non-agonistic behaviors during the first 15 days. Both the frequency and types of interaction were shown to vary according to the type of group. Two species that share a common habitat are less aggressive and display more non-agonistic behavior than when the species come from different habitats. On the other hand, although aggressive behaviors increase with greater phyletic distance between the species, non-agonistic interactions remain constant.As a general rule, interactions between species from differing environments seem to be determined by the phyletic distance, whereas those between species from the same biotope are controlled by interspecific competition. There is a gradual change in these interactions dependent on the duration of the mixed association.     

Variation in mate recognition specificities among four Callosobruchus seed beetles

Differentiation of mate recognition systems is one of the important steps for speciation in animals. For some insects, a contact sex pheromone present on the cuticular surface is indispensable in discriminating reproductive partners. In Callosobruchus species (Coleoptera: Chrysomelidae: Bruchinae), contact sex pheromones have been found in two species, Callosobruchus chinensis (L.) and Callosobruchus maculatus (Fabricius). It was suggested, however, that these two species lacked the ability to discriminate their conspecific and/or heterosexual partners. To elucidate this inconsistency, we verified the existence of contact sex pheromones from two other species, Callosobruchus rhodesianus (Pic) and Callosobruchus analis (Fabricius). As a result, unlike C. chinensis and C. maculatus, the males of C. rhodesianus and C. analis were able to discriminate their heterosexual partners. Comparing cross‐copulation behavior, i.e., copulation behavior between two species, against these four species indicated that the mate recognition specificities were quite different. Males of C. rhodesianus and C. analis had highly species‐specific mating behavior, whereas males of C. chinensis and C. maculatus were much less specific. These results indicate that variation in mate recognition can arise even among congeneric species living in a sympatric environment, and this variation might have arisen during species differentiation. Based on our results in combination with previous reports on interspecific competition, we suggest that the observed asymmetric cross‐copulation behavior might be, at least partially, an adaptation for surviving interspecific competition.     

Natural hybridization of two mussel species <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas, 1771) and <Emphasis Type="Italic">Dreissena bugensis</Emphasis> (Andrusov, 1897)

Dreissenids display a high diversity of shell morphology, and it is frequently difficult to ascribe some individuals from mixed populations to one of the two species, Dreissena polymorpha (Pallas, 1771) or D. bugensis (Andrusov, 1897). Presumably, such individuals may be interspecific hybrids. We have analyzed species-specific allozyme loci of the typical representatives of these two mussel species and putative interspecific hybrids. A natural interspecific hybrid between D. polymorpha and D. bugensis was discovered for the first time by genetic methods. It has been demonstrated that D. bugensis was a maternal parent.     

Species composition and correlation of understory woody plants in Chinese fir plantation in the lower subtropical area

There are 71 species in the shrub layer of the Cunninghamia lanceolata plantation after natural succession. The species richness and diversity have increased with slight anthropogenic disturbance. The status and function of understory woody species were judged by the analysis of the important value (IV). x ² statistics and r test were used for testing the significance of interspecific association and correlation among 25 main understory woody plants selected from the woody population. The results clearly showed their interspecific relationships and their differences in resource utilization. Species-pairs of positive association were in the majority. Most species were accommodated in the shady habitat. There was a positive correlation between the IV of the species and the interspecific association. The higher the IV of the species, the closer and more significant was the interspecific association. Based on analytical results of interspecific association and correlation, 25 woody plants in the shrub layer could be divided into four ecological species groups: I. Ficus hispida + Antidesma bunius + Mallotus barbatus + Ficus cunia + Saurauia tristyla + Mallotus philippinensis + Maesa japonica + Ficus hirta + Alchornea rugosa + Ficus fulva + Mallotus apelta; II. Cudrania tricuspidata + Schefflera octophylla; III. Cunninghamia lanceolata + Clerodendron cytophyllum + Millettia semicastrata + Randia spinosa + Litsea cubeba + Litsea pungens; IV. Ardisia japonica + Psychotria rubra + Vitex quinata + Cephalanthus occidentalis + Pithecellobium lucidum + Mycetia sinensis. If species group III or II is the advantaged species in the shrub layer, the community would change from a coniferous forest to a sparse evergreen broad-leaved forest. For group IV, the community would be relatively stable. For group I, the coniferous forest would be mixed with coniferous-broad leaved forest. The classification of ecological species groups would provide a theoretical basis on judging its ecological function, adjusting the stand structure of the plantation and directing the suitable natural vegetation type through the close-natural restoration process. __________ Translated from Acta Ecologica Sinica, 2005, 25(9): 2173–2179 [译自: 生态学报, 2005, 25(9): 2173–2179]     

Intra- and interspecific host discrimination in two closely related egg parasitoids

Intraspecific host discrimination is frequently found in solitary parasitoids, but interspecific host discrimination, where female parasitoids recognize hosts already parasitized by females of other species, is rare. This particular behaviour appears to be adaptive only under specific circumstances. In this paper, we quantified intraspecific host discrimination in Anaphes n. sp. (Hymenoptera: Mymaridae), an endoparasitoid of the eggs of Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) and interspecific host discrimination toward eggs parasitized by Anaphes sordidatus (Girault), a sympatric species competing for the same resource in similar habitats. To examine host discrimination, choice experiments were used where the females had to choose between different categories of eggs (unparasitized, parasitized by Anaphes n. sp. or A. sordidatus). Superparasitism and multiparasitism were avoided in experiments where the female had a choice between unparasitized hosts and hosts parasitized by the same female, by a conspecific or by a female A. sordidatus. When all hosts available were parasitized, conspecific superparasitism occurred more often than self-superparasitism or multiparasitism. These results indicated that females Anaphes n. sp. were capable of self-, conspecific and interspecific discrimination. Self-discrimination followed recognition of an external marking while interspecific discrimination occurred mostly after insertion of the ovipositor. Interspecific discrimination could result from the recent speciation of these species and could be associated with a genotypic discrimination. This behavior appears to be adaptive because of the competition for common hosts between the two parasitoid species.     

On the Advantages of Mixed‐Species Groups: Impalas Adjust Their Vigilance When Associated With Larger Prey Herbivores

Prey can obtain valuable benefits from associating with other species if heterospecifics help to detect predators or locate good food patches. In mixed‐species groups, how species respond to the presence of other species remains a poorly explored question although it might give crucial insights into mechanisms underlying the interspecific coexistence. We studied temporary mixed‐species groups of large herbivores in Hwange National Park (Zimbabwe) between the common impala (Aepyceros melampus), the focal species here, and bigger species including the plains zebra (Equus quagga), the greater kudu (Tragelaphus strepsiceros) or the blue wildebeest (Connochaetes taurinus). In the Hwange savanna, the focal and smaller species are exposed to a larger range of predators than the associated species. In this context, we investigated how impalas adjusted their vigilance with group size comparing impala‐only and mixed‐species groups and whether the identity of heterospecifics affected vigilance of impalas. Our study showed that the time impalas spent in vigilance significantly decreased with group size when they formed impala‐only groups, whereas it did not significantly vary with group size in mixed‐species groups. Moreover, in mixed‐species groups, impalas did not adjust their time spent in vigilance with the proportion of conspecifics and the identity of the associated species. Thus, the mechanism underlying the difference of impalas' behavioural adjustment of vigilance with group size between single‐ and mixed‐species groups seemed to be related to the presence but not to the number and the identity of heteropecifics. Finally, we discuss the concept that larger and dominant heterospecifics were likely to increase competition for food access, thereby forcing higher vigilance of impalas, outweighing any reduction from collective vigilance.     

Blunt egg pole holds cues for alien egg discrimination: experimental evidence

Eggshell colour patterns play a crucial role in avian host–parasite coevolution. In contrast to many experiments investigating general host egg discrimination abilities, studies testing where specific recognition cues are located on the eggshells (on blunt, sharp or both egg poles) are lacking. Previous studies suggested that discrimination cues might be located at the blunt egg pole, where the shell patterning is typically concentrated. We tested this hypothesis experimentally in species subject to interspecific (great reed warblers Acrocephalus arundinaceus, reed warblers A. scirpaceus), and also intraspecific parasitism (song thrushes Turdus philomelos, blackbirds T. merula). We examined host responses towards two types of intraspecific eggs painted non‐mimetic immaculate blue either at blunt or sharp poles. All four species rejected eggs manipulated at the blunt pole at significantly higher rates, indicating that they perceive the critical recognition cues in the same egg part. Thus, the presence of egg recognition cues at the blunt egg pole may be a general phenomenon in birds parasitized by both intraspecific and interspecific parasites.     

Species and Colony Components in the Recognition Odor of Young Social Wasps: Their Expression and Learning (Polistes biglumis and P. atrimandibularis; Hymenoptera: Vespidae)

In Polistes, nestmate recognition relies on the learning of recognition cues from the nest. When wasps recognize nestmates, they match the template learned with the odor of the encountered wasp. The social wasp Polistes biglumis use the homogeneous odor of their colony to recognize nestmates. When these colonies become host colonies of the social parasite P. atrimandibularis, colony odor is no longer homogeneous, as the parasite offspring have an odor that differs from that of their hosts. In trying to understand how the mechanism of nestmate recognition works in parasitized colonies and why parasite offspring are accepted by hosts, we tested the responses of resident Polistes biglumis wasps from parasitized and unparasitized colonies to newly emerged parasites and to nestmate and non-nestmate conspecifics. The experiments indicate that immediately upon eclosion both young parasites and young hosts lack a colony odor and that colony odor can be soon acquired from the accepting colony. In addition, while residents of nonparasitized colonies recognize only the odor of their species, resident hosts of parasitized colonies have learned a template that fits the odors of two species.     

Immigration and formation of mixed colonies in red wood ants (Hymenoptera,Formicidae)

Long-term field studies of the composition and spatial structure of settlements of ants of the Formica rufa group were carried out in two regions of Russia (Moscow and Arkhangelsk provinces). Fragmentation of damaged nests followed by reintegration of the fragments is the main way of formation of mixed colonies of ants from different nests (including different species). The principal factor of nest fragmentation is their damage by wild boars, bears, and in some localities, by poachers. The formation of mixed nests and nest complexes with participation of different Formica species was observed. They are formed by joining the ants from several damaged nests or by a colony from a destroyed nest immigrating into an intact one. Regular damage of many nests leads to the formation of broad zones of mixed colonies. The mixed colonies including 2–3 species of wood ants have recently become common. The phenomenon of mixed colonies raises a question as to the relative importance of two basic principles (sociality and specific identity) in the life of ant societies and demonstrates the priority of the social principle.     

Outlier loci highlight the direction of introgression in oaks

Loci considered to be under selection are generally avoided in attempts to infer past demographic processes as they do not fit neutral model assumptions. However, opportunities to better reconstruct some aspects of past demography might thus be missed. Here we examined genetic differentiation between two sympatric European oak species with contrasting ecological dynamics (Quercus robur and Quercus petraea) with both outlier (i.e. loci possibly affected by divergent selection between species or by hitchhiking effects with genomic regions under selection) and nonoutlier loci. We sampled 855 individuals in six mixed forests in France and genotyped them with a set of 262 SNPs enriched with markers showing high interspecific differentiation, resulting in accurate species delimitation. We identified between 13 and 74 interspecific outlier loci, depending on the coalescent simulation models and parameters used. Greater genetic diversity was predicted in Q. petraea (a late‐successional species) than in Q. robur (an early successional species) as introgression should theoretically occur predominantly from the resident species to the invading species. Remarkably, this prediction was verified with outlier loci but not with nonoutlier loci. We suggest that the lower effective interspecific gene flow at loci showing high interspecific divergence has better preserved the signal of past asymmetric introgression towards Q. petraea caused by the species' contrasting dynamics. Using markers under selection to reconstruct past demographic processes could therefore have broader potential than generally recognized.     

Differential effect of inter- and intraspecific competition on the performance of invasive and native Taraxacum species

Inter- and intraspecific competitive abilities are significant determinants of invasive success and the ecological impact of non-native plants. We tested two major hypotheses on the competitive ability of invasive species using invasive (Taraxacum officinale) and native (T. platycarpum) dandelions: differential interspecific competitive ability between invasive and native species and the kin recognition of invasive species. We collected seeds from two field sites where the two dandelion species occurred nearby. Plants were grown alone, with kin (plants from the same maternal genotype) or strangers (plants from different populations) of the same species, or with different species in a growth chamber, and the performance at the early developmental stage between species and treatments was compared. The invasive dandelions outcompeted the native dandelions when competing against each other, although no difference between species was detected without competition or with intraspecific competition. Populations of native species responded to interspecific competition differently. The effect of kinship on plant performance differed between the tested populations in both species. A population produced more biomass than the other populations when grown with a stranger, and this trend was manifested more in native species. Our results support the hypothesis that invasive plants have better competitive ability than native plants, which potentially contributes to the establishment and the range expansion of T. officinale in the introduced range. Although kin recognition is expected to evolve in invasive species, the competitive ability of populations rather than kinship seems to affect plant growth of invasive T. officinale under intraspecific competition.     

Analysis of interactions between the invasive tree-of-heaven (<Emphasis Type="Italic">Ailanthus altissima</Emphasis>) and the native black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis>)

Invasive exotic plants can persist and successfully spread within ecosystems and negatively affect the recruitment of native species. The exotic invasive Ailanthus altissima and the native Robinia pseudoacacia are frequently found in disturbed sites and exhibit similar growth and reproductive characteristics, yet each has distinct functional roles such as allelopathy and nitrogen fixation, respectively. A four-month full additive series in the greenhouse was used to analyze the intraspecific and interspecific interference between these two species. In the greenhouse experiment, the inverse of the mean total biomass (g) response per plant for each species was regressed on the density of each species and revealed that the performance of the plants was significantly reduced by interspecific interference and not by intraspecific interference (p < 0.05). Other biomass traits such as root dry weight, shoot dry weight, stem dry weight, and leaf dry weight were also negatively affected by interspecific interference. Competition indices such as Relative Yield Total and Relative Crowding Coefficient suggested that A. altissima was the better competitor in mixed plantings. Ailanthus altissima consistently produced a larger above ground and below ground relative yield while R. pseudoacacia generated a larger aboveground relative yield in high density mixed species pots.     

Nest recognition in neighboring colonies: a comparison of two European species of Polistes wasps (P. dominulus and P. nimphus, Hymenoptera: Vespidae)

The ability of two species of Polistes wasps to distinguish their own from nearby nests was tested, following the procedure used by Espelie et al. Our experiments demonstrated that, in the laboratory, females of Polistes dominulus and Polistes nimphus preferentially selected their own nests rather than nearby nests. We also evaluated the role of odor cues in nest recognition by washing nests in hexane to remove the apolar solvent-soluble components of nest odor. Although P. nimphus females continued to discriminate nests even after washing, P. dominulus individuals failed to discriminate between their own and a foreign neighboring nest. In both species, wasps were able to recognize their own nests when nest extracts were subsequently reapplied to the nest surface. These results indicate that P. dominulus wasps recognize their nests through perception of nest odor. The ability of P. nimphus wasps to distinguish their own nests even after presumed removal of the nest odor is discussed. Received: January 27, 2000 / Accepted: May 22, 2000     

Developmental Time and Thorax Length Differences Between the Cactophilic Species Drosophila Buzzatii and D. Koepferae Reared in Different Natural Hosts

Drosophila buzzatii and Drosophila koepferae are two cactophilic sibling species whose ranges partially overlap in Northwestern and Western Argentina. Both species can utilize the decaying tissues of both Opuntia and columnar cacti as breeding sites. Though D. buzzatii and D. koepferae are not differentially attracted to Opuntia and columnar hosts, the composition of the communities of flies emerging from natural substrates of both cacti differed significantly in a natural population. The objective of this paper is to analyze whether intra and/or interspecific competition affects development time and thorax length in D. buzzatii and D. koepferae when both species are reared in single and mixed species culture and fed with semi-natural media prepared with fermenting materials of Opuntia sulphurea(tuna) and Trichocereus terschekii(cardón). Our results showed that both traits differ significantly between flies raised in different hosts and that differences between D. koepferae and D. buzzatii species for both thorax length and development time depend on the type of culture (mixed vs. single species). In addition, the host by type of culture interaction was significant. We also observed thorax length differences between Drosophila species and type of culture. Our present data suggest that the effect of intra and interspecific competition varied between the two traits investigated and between species. However, competition alone cannot explain the differential pattern of resource utilization shown by D. buzzatii and D. koepferae in the natural population studied.     

Interspecific body size differentiation in species assemblages of the carabid subgenus Ohomopterus in Japan

Geographic variation and interspecific differentiation in body size (body length) were analyzed for 15 species of the carabid subgenus Ohomopterus (genus Carabus; Coleoptera, Carabidae) in Japan. Local species assemblages of this subgenus consist of up to 5 species of different size classes. These beetles exhibited sexual dimorphism in body size where females are larger than males, except Carabus uenoi, in which the male and female sizes were equivalent, possibly because of the exaggerated male genitalia. In 9 of 15 species, there was a positive correlation between mean body size and annual mean temperature of habitat, representing the converse of Bergmann's rule. However, in some cases this correlation does not hold over the range of a species because of regional differences. When allopatric and sympatric populations were compared, allopatric populations of Carabus albrechti and C. japonicus had larger bodies than sympatric populations. These intraspecific differences may have resulted from character displacement. In each local assemblage with 2 or more species, there was little interspecific overlap of body size, although the body size ratio between two species with adjacent body sizes seldom showed strict constancy. The mean size ratio between 2 adjacent species in an assemblage was reduced with the number of species, whereas the size ratio of the largest to smallest species in an assemblage increased with the number of species (i.e., the expansion of body size range). These results indicate that the body size of Ohomopterus species may have evolved in response to both climatic conditions and interspecific interactions. Because each species or species group represents the same size class over the distribution range and similar-sized species are parapatric or allopatric, the interspecific segregation in body size in local assemblages may have resulted mainly from a size assortment process during colonization. Received: June 8, 2000 / Accepted: October 10, 2000     

The effect of interspecific mating on sex ratios in the twospotted spider mite and the Banks grass mite (Acarina: Tetranychidae)

Mixed populations of the twospotted spider mite (TSM),Tetranychus urticae (Koch), and the Banks grass mite (BGM),Oligonychus pratensis (Banks), occur on corn and sorghum plants in late summer in the Great Plains. Interspecific matings between these arrhenotokous species occur readily in the laboratory but yield no female offspring. The effect of interspecific mating on female: male sex ratios was measured by examining the F₁ progeny of females that mated with both heterospecific and conspecific males in no-choice situations. TSM females that mated first with BGM males and then with TSM males produced a smaller percentage of female offspring than TSM females that mated only with TSM males (43.1±5.8 and 78.9±2.8% females, respectively). Similarly, BGM females mated with heterospecific males and then with conspecific males produced fewer female offspring than females mated only with BGM males (55.7±5.2 and 77.5±2.5%, respectively). Lower female: male sex ratios were produced also by BGM females that mated with TSM males after first mating with conspecifics (62.4±3.4%). In mixed populations containing males of both species, females also produced lower female: male sex ratios, but these ratios were not as low as expected based on mating propensities and progeny sex ratios observed in no-choice tests. These data suggest that interspecific mating may substantially reduce female fitness in both mite species by reducing the output of female offspring, but in mixed populations this effect is mitigated by unidentified behavioral mechanisms.     

Mate discrimination in Littorina littorea (L.) and L. saxatilis (Olivi) (Mollusca:Prosobranchia)

The ability of males of Littorina littorea and L. saxatilis to discriminate between mates of different sex, species and size was examined. In partner choice experiments males of L. littorea had the possibility to initiate a copulation with either a female or a male. The males did not show a preference for either sex. There was therefore no evidence that they could determine the sex of a conspecific prior to copulation. The duration of intrasexual copulation was considerably shorter than for intersexual copulation, both in the field and in laboratory experiments. For the two species, intersexual copulations were far more frequent than intrasexual ones. This can partly be explained by the difference in copulation time.Few interspecific copulating pairs were found on the shore. This may reflect a low interspecific encounter rate rather than a mechanism of species recognition. On all of these occasions, however, the active male was of L. saxatilis. It is argued that selection against precopulatory species and sex recognition is a more likely explanation than an hypothesis that states that the required mutations for precopulatory mate identification has not yet occurred. L. littorea males copulated longer with large than with small females. Copulation time was short with parasitized females, which are sterile or of low fecundity. The allocation of mating effort by males is discussed.