摘要:

This paper describes the morphological and behavioural adaptations responsible for ant‐like appearance in eight species (generaZuniga, Synemosyna, Sphecotypus,andMyrmecium)of salticid and clubionid spiders studied in Amazonian and SE Brazil. All ant‐mimicking spiders have body and legs thin, and the shiny integument typical of their models. Light horizontal hair bands and constrictions of the cephalothorax and abdomen simulate, respectively, the head‐thorax joint and segmented gaster of ants. The petiole and postpetiole of the ants are usually mimicked by a lengthened pedicel, together with a narrowing of the posterior cephalothorax and/or anterior abdomen. The prominent pedipalps of the spiders often simulate ant mandibles, but they may also be strikingly similar to an ant's head. All ant‐mimicking spiders walked in a zig‐zag ant‐like pattern, and frequently raised and moved about the first pair of legs as ‘antennae’. The mimics were found in the same microhabitats (foliage or ground) as their models, and displayed strong avoidance reactions toward the latter both in the field and in captivity. The inoffensive characteristics of the mimics and the noxious traits of their models (strong mandibles, potent sting, hard integument, venomous secretions) strongly suggest that the spiders are Batesian ant‐mimics. The detailed structural and behavioural adaptations enhancing ant‐mimicry provide strong circumstantial evidence that the selective agents involved must have good visual acuity, and are probably small insectivorous vertebrates (e.g. birds, lizards and toads) or arthropods (e.g. wasps and spider

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00443.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The pupae of the tropical butterflyDanaus chrysippusare either green or pink the switch being operated by a ‘greening’ hormone produced in the larval head. Both environmental and genetic cues are involved in controlling the endocrine mechanism.The environmental factors identified are of two distinct kinds: proximate factors influence pupal colour after the larva has selected its pupation site, whereas ultimate factors are effective at an earlier stage, either prompting choice of pupation site by the larva or priming pupation physiology in a particular direction. Genetic factors preadapt the larva to form a pupa which will be cryptic in the normal or average conditions, climatic or biogeographical, anticipated in its environment.The proximate factors demonstrated are background colour, darkness, light quality (wavelength) and humidity. There is some evidence that substrate texture may also be relevant. Ultimate factors are temperature, humidity and species of larval foodplant. Two closely linked gene loci which govern the phenotype of adult morphs and races either have a pleiotropic effect on pupa colour or are closely linked with other genes which do so. Moreover, the two loci interact epistatically with respect to their pupation effects.Factors producing predominantly green pupae are plant substrates, yellow background, darkness, yellow light, high humidity, high temperature, theballele at the B locus when homozygous and, on non‐plant substrates, theCallele at the C locus. High frequencies of pink pupae result on non‐plant substrates, red backgrounds, in blue light, low humidity, low temperatures and inB‐andccgenotypes. The C locus alleles,Candc,interact epistatically with the B alleles, their effect on choice of pupation site being determined by linkage phase. Of the two foodplants tested,Calotropisproduced a high frequency of green pupae andTylophoraof pinks. The seasonal cycling of rainfall, temperature, availability or condition of foodplant, and gene frequencies are all correlated with oscillations in the frequencies of green and pink pupae. Though genotype influences pupa colour, all genotypes are capable of forming pupae of both colours. The variation can therefore be attributed to an environmental polyphenism superimposed upon a genetic polymorphism.The hormone producing green pupae emanates from the head during the prepupal period. Denied hormonal influence, the pupa is pink. Pupal colour is judged to be aposematic at close range and cryptic at

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00444.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The relationship between the butterfly genusEuphilotesand their host plant genusEriogonumin western North America is suggested to be one of sequential evolution rather than coevolution.Eriogonum,a genus of nearly 250 species, probably had a Miocene origin, but has had its modern distribution significantly influenced by recent Pleistocene glaciation. The evolutionof Euphilotes,as a distinct genus of four sibling species, apparently postdates the establishment and recent proliferation ofEriogonum.Successful speciation inEuphiloteshas been accomplished mainly through modifications in genitalia of those butterflies using a single species ofEriogonum.The subsequent proliferation ofEuphilotessubspecies has been the result of host switching coupled with geographic isolation onto individual speciesof Eriogonumacting as restricted biogeographic islands. In the first instance, direct evolutionary competition for a limited resource (one species ofEriogonum)leads to partitioning of that resource by the butterflies whose entire life cycle is associated with that plant species. In the second instance, host switching and isolation have permitted establishment of minor subspecies without significant interaction with other subspecies of the same species. In instances where interspecific subspecies competition exists, resource partitioning, coupled with more pronounced genetic isolation, seem to have occurred resulting in more readily distinct subspecies. We speculate that the success of subspeciation inEuphilotesis dependent upon the numeric size and geographic extent of the host species.Euphilotessubspecies on plants of restricted distributions are themselves seemingly limited in their evolutionary potential as the most dynamic evolution ofEuphilotessubspecies is that associated with widespread and variableEriogonumspecies. In all instances, the tempo and mode of evolution inEuphilotesappears to be sequential as it follows and is seemingly dependent upon what has already occurred inEriogonum.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00445.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb00443a.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY