Alternative adaptations, speciation, and phylogeny (A Review)

Abstract

Alternative adaptations-different adaptive phenotypes maintained in the same life stage and the same population but not necessarily simultaneously expressed in the same individual-represent contrasting character sets produced by the same genome, in effect allowing a single species to occupy more than one sympatric niche. Such alternatives are particularly likely to give rise to novel adaptations because of selection for extreme dissimilarity between them and because established traits buffer populations against extinction while independently expressed alternatives evolve in new directions. Particular alternatives can be suddenly fixed in populations with little or no genetic change, leading to a period of rapid evolution (especially, of morphology) exaggerating the characteristics of the newly fixed form. This burst of change would facilitate rapid speciation and could produce "punctuated" patterns of evolution. Evidence from a wide variety of organisms shows that alternative phenotypes are exceedingly common in nature and that they are probably important in speciation and macroevolution. Although many of these ideas and observations have been noted piecemeal by previous authors, bringing them together demonstrates the probable importance of alternative adaptations in the origin of major evolutionary novelties and calls for a revision of current and traditional ideas about the role of behavior and ontogeny in the genesis of organic diversity.The Alternative-Adaptation HypothesisThe purpose of this paper is to suggest a change in the way biologists think about the origins of organic diversity: character divergence, speciation, and macroevolution or the invasion of major new adaptive zones.The usual way to visualize phylogenetically important divergence begins with reproductive isolation, or speciation: a branching point of a phylogenetic tree marks both the beginning of a new lineage and the beginning of character divergence. New characters may conceivably arise without reproductive isolation via gradual evolution over time, with the eventual formation of a new "chronospecies". But increased diversity and major innovation begin with speciation, and macroevolution leading to the origin of a new higher taxon requires a series of such events. On this evolutionists have generally agreed, even when holding otherwise disparate opinions (e.g., see p. 524 of ref.

A review of deviant phenotypes in bees in relation to brood parasitism, and a gynandromorph of Megalopta genalis (Hymenoptera: Halictidae)

“…Although it is unlikely that such freaks were themselves ancestral to a parasitic species or lineage, they point to mechanisms that might make elements of a parasite-like morphology recurrently available for selection when pollen-collecting females behave facultatively as parasites (e.g. Wcislo, 1987;Field, 1992;West-Eberhard, 1986). In a review of the morphology and behaviour of parasitic sweat bees (Halictinae), Michener (1978) describes how some characteristics of female parasites phenetically resembled males of their hosts or close relatives (table 1), and the list could be extended by including additional traits that are found only in certain taxa (e.g.…”

Evolution of adaptive phenotypic traits without positive Darwinian selection

“…Along with earlier ideas, such as those of Baldwin (1896), the importance of genetic assimilation in evolution remained controversial, largely because there was no clear understanding of the underlying genetic mechanism (Crispo, 2007). This concept was revived in a modern context in the groundbreaking work of West-Eberhard (1986, who pointed out that phenotypic plasticity might often precede the evolutionary origin of an evolved adaptation. Similar ideas have been developed by Pigliucci and Murren (2003), Pigliucci et al (2006) and Pfennig et al (2010).…”

Larval growth in polyphenic salamanders: making the best of a bad lot

“…Polyphenisms provide model systems for the study of phenotypic variation because: (1) the trait of interest has a direct environmental component; (2) alternative phenotypes are often distinct and easily distinguished; and (3) they are likely to be a direct result of selection (Caswell 1983;Smith-Gill 1983). Documenting the ecological and evolutionary contexts that produce and maintain polyphenisms is critical for understanding their role in speciation, life history evolution, the maintenance of biodiversity, and the evolution of plasticity (West-Eberhard 1986, 2003Hazel et al 1990;Via 2001;Denoël et al 2005;Emlen et al 2007;Pfennig et al 2007Tomkins and Hazel 2007;Pfennig and McGee 2010).…”

“…Environmentally-cued polymorphisms (polyphenisms), which occur when discretely different phenotypes develop from genotype by environment interactions, provide excellent opportunities for understanding the mechanisms producing and maintaining phenotypic variation and plasticity (West-Eberhard 1986, 2003Hazel et al 1990Hazel et al , 2004Scheiner 1993;Roff 1996;Relyea 2002;Tomkins and Hazel 2007). Polyphenisms provide model systems for the study of phenotypic variation because: (1) the trait of interest has a direct environmental component; (2) alternative phenotypes are often distinct and easily distinguished; and (3) they are likely to be a direct result of selection (Caswell 1983;Smith-Gill 1983).…”