摘要:

Some species of the paleotropical tree genusMacaranga(Euphorbiaceae) live in close association with ants. The genus comprises the full range of species from those not regularly inhabited by ants to obligate myrmecophytes. In Malaysia (Peninsular and Borneo) 23 of the 52 species are known to be ant‐associated (44%). The simplest structural adaptation of plants to attract ants are extrafloral nectaries. We studied the distribution of extrafloral nectaries in the genusMacarangato assess the significance of this character as a possible predisposition for the evolution of obligate myrmecophytism. All species have marginal glands on the leaves. However, only the glands of non‐ myrmecophytic species function as nectaries, whereas liquids secreted by these glands in myrmecophytic species did not contain sugar. Some non‐myrmecophyticMacarangaand transitionalMacarangaspecies in addition have extrafloral nectaries on the leaf blade near the petiole insertion. All obligatorily myrmecophyticMacarangaspecies, however, lack additional glands on the lamina. The non‐myrmecophytic species are visited by a variety of different ant species, whereas myrmecophyticMacarangaare associated only with one specific ant‐partner. Since these ants keep scale insects in the hollow stems, reduction of nectary production in ant‐inhabitedMacarangaseems to be biologically significant. We interpret this as a means of (a) saving the assimilates and (b) stabilization of maintenance of the association's specificity. Competition with other ant species for food rewards is avoided and thereby danger of weakening the protective function of the obligate ant‐ partner for the plant is reduced.A comparison with other euphorb species living in the same habitats asMacarangashowed that in genera in which extrafloral nectaries are widespread, no myrmecophytes have evolved. Possession of extrafloral nectaries does not appear to be essential for the development of symbiotic ant‐plant interactions. Other predispositions such as nesting space might have played a more

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00621.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Much phylogenetic information has been derived from the analysis of sequence similarity in genes and proteins. These data are generally considered to be more reliable than an examination of the phylogenetic distribution of similar biologically active molecules. However, molecules can provide significant phylogenetic information when accompanied by a careful analysis of their structure, synthesis, genetics and function. Molecules may be highly structurally and functionally constrained. Thus, similar or even chemically identical molecules may be unrelated, and this may be discernible only by examination of information beyond the simple structure of the molecule. Phylogenetic variation in the synthesis of tyrosine and lysine demonstrates that chemical identity of molecules may be brought about by unrelated synthetic pathways. The widespread distribution of collagen triple helices is shown to result from convergence under structural and functional constraints. This is demonstrated by an examination of the steric constraints upon collagens and the presence of several independent families of collagen genes. Lysyl oxidase crosslinking occurs in several unrelated proteins, indicating that similarity in the post‐translational modification of proteins is not evidence of homolog

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00622.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Understanding rules of resource allocation within individuals is helpful in explaining population dynamics. This is particularly the case under the conditions of resource limitation that are commonly experienced by zooplankton. Here, we evaluate assumptions underlying models of resource allocation inDaphniaand test the predictions of two models of response to starvation.We also test the predictions of two simple models concerning the mechanisms of egg provisioning inDaphnia magna.Our results: (1) demonstrate that provisioning is discontinuous, occurring over a discrete period of the instar; (2) support the hypothesis that egg production occurs in a serial fashion; (3) show thatDaphnia magnaresponds to starvation by ceasing egg production but that there is an increase in mean size of eggs provisioned during the instar, prior to starvation; and (4) broadly support predictions that the response ofDaphniato starvation is an instantaneous cessation of reproduction but that there is a time lag before death.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00623.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

A review of the larval hostplant associations of African and Australian butterflies highlights their overall conservatism in host choice—the most widely exploited families are cosmopolitan or pan‐ tropical in range. Thus there is no apparent relationship between butterfly diversity and endemic plant novelty at the family level. Such conservatism in hostplant preferences suggests that butterflies encounter few opportunities to make gross hostplant shifts, with the likelihood of the limited available options being repeatedly explored through time. Attempts to detect any simple parallel cladogenesis between butterflies and their larval hosts must allow for the probability of homoplasy. Similarities in the host ranges of the Papilionoidea, Hesperioidea and Hedyloidea might suggest that the Malvales constitute the ancestral host group of the butterfl

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00624.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Faunal assembly in chironomids was analysed using published data in the fauna of three rivers in southern England and of Great Britain as a whole. Two questions, both relating to the generic composition of local faunal assemblages, were asked: (i) to what extent are faunas from different sites within a single geographical area associated in terms of the occurrence of genera (‘generic association’); (ü) given the total number of species observed, is the number of different genera represented (‘generic spread’) more than would be expected by chance. The latter question relates to the hypothesis that if interspecific competition is a strong organizing force of local faunal assemblages, species would be more likely to occur as widely spread out among different genera, thus decreasing overlap in resource use and hence the possibility of outright competition. Null models of species occurrence were constructed through Monte Carlo simulation to evaluate quantitatively these two questions. Generic association of faunal assemblages from three localities was statistically significant, though there was some variation among different subfamilies of Chironomidae. No evidence of generic diversification (more genera occurring in the fauna than expected by chance) was found. These results and the original questions were given critical considerations in the di

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00625.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The perennial salt marsh grassSpartina anglicais one of the classic examples of allopolyploid speciation. It originated on the south coast of England at the end of the nineteenth century following chromosome doubling inS. × townsmdii, a hybrid between the native BritishS. marilimaand a species introduced from the United States,S. alterniflora.The nature of the origin ofS. anglicais beyond doubt; however, it is not known whether it had a single or multiple origin. In order to address this problem we undertook a survey of the genetic variation in the parental species ofS. anglicausing isozyme electrophoresis. The results show thatS. alterniflorahas no detectable variation and thatS. maritimahas extremely low levels of variation. These results, unfortunately, prevent the question of a single or multiple origin from being answered. Possible reasons for the low levels of variation and its influence on the future of the species are discussed. Another problem concerning the parental species is the rapid decline ofS. maritimain Britain. It is often assumed that the major factor in this regression is the invasion of its habitats byS. anglica.We have examined the status of S.marilimathroughout its range in Britain and have found thatS. anglicararely co‐occurs withS. maritima.We propose that the decline ofS. maritimais largely due to the physical erosion of its habitats and that this erosion may produce suitable habitats for colonization byS. angli

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00626.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Quantitative genetic variation was assessed in a population ofCrepis tectorumsubsp.pumila, a winter annual confined to calcareous grassland on the Baltic island of öland (SE Sweden). Plants from 40 maternal sibships were grown in a greenhouse and scored for a large number of traits representing all stages of the life cycle. The study included several characters that have been subject to ecotypic differentiation as well as traits known to be under current selection. Highly significant family differences were found for all but one character, suggesting that past selection was too weak to eliminate the genetic variability of characters presumed to be adaptive and there is a potential for further adaptive change in most traits. Two additional traits treated as qualitative were also found to differ significantly among families. A parallel cultivation experiment showed that the extent of population divergence in a quantitative trait was positively correlated with the amount of inter‐ family variation, implying stability of the relative variability for substantial periods of time, a possible reflection of phenotypic constraints being expressed both within and between populations. Additional data indicated that genetic trade‐offs among traits under simultaneous selection, year‐to‐ year variation in selection in combination with a long‐lived seed bank, and genotype × environment interactions, could prevent the erosion of genetic variability in some characters connected w

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1991.tb00627.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY