Since the Age of Exploration began, there has been a drastic breaching of biogeographic barriers that previously had isolated the continental biotas for millions of years. We explore the nature of these recent biotic exchanges and their consequences on evolutionary processes. The direct evidence of evolutionary consequences of the biotic rearrangements is of variable quality, but the results of trajectories are becoming clear as the number of studies increases. There are examples of invasive species altering the evolutionary pathway of native species by competitive exclusion, niche displacement, hybridization, introgression, predation, and ultimately extinction. Invaders themselves evolve in response to their interactions with natives, as well as in response to the new abiotic environment. Flexibility in behavior, and mutualistic interactions, can aid in the success of invaders in their new environment.

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The evolutionary impact of invasive species.

The evolutionary genetics of invasive species has been relatively unexplored, but could offer insights into mechanisms of invasions. Recent studies suggest that the invasion success of many species might depend more heavily on their ability to respond to natural selection than on broad physiological tolerance or plasticity. Thus, these studies stress the importance of genetic architecture, selection upon which could result in evolutionary adaptations and possibly speciation. For instance, epistatic interactions and the action of a few genes could facilitate invasion success. These findings emphasize the utility of genomic approaches for determining invasion mechanisms, through analysis of gene expression, gene interactions, and genomic rearrangements that are associated with invasion events.

Evolutionary genetics of invasive species

In six bird species convenient for study, niches are known to be broader on some islands than on the mainland. In every case there is also greater variation in a bill measurement on the islands, except for one species in which the niche on the Canary Islands is narrower than that on the mainland. The adjusted variances average about twice as great in the broader niche. These and other results suggest that continuous variation within local populations is often adaptive in itself and is not part of the genetic or phenotypic load.

Morphological variation and width of ecological niche

The introduction and rapid spread of Drosophila subobscura in the New World two decades ago provide an opportunity to determine the predictability and rate of evolution of a geographic cline. In ancestral Old World populations, wing length increases clinally with latitude. In North American populations, no wing length cline was detected one decade after the introduction. After two decades, however, a cline has evolved and largely converged on the ancestral cline. The rate of morphological evolution on a continental scale is very fast, relative even to rates measured within local populations. Nevertheless, different wing sections dominate the New versus Old World clines. Thus, the evolution of geographic variation in wing length has been predictable, but the means by which the cline is achieved is contingent.

/pdf/rapid-evolution-of-a-geographic-cline-in-size-in-an-5enqgvi3yb.pdf

Rapid evolution of a geographic cline in size in an introduced fly.

The comparative analysis of homologous characters is a staple of evolutionary developmental biology and often involves extrapolating from experimental data in model organisms to infer developmental events in non-model organisms. In order to determine the general importance of data obtained in model organisms, it is critical to know how often and to what degree similar phenotypes expressed in different taxa are formed by divergent developmental processes. Both comparative studies of distantly related species and genetic analysis of closely related species indicate that many characters known to be homologous between taxa have diverged in their morphogenetic or gene regulatory underpinnings. This process, which we call "developmental system drift" (DSD), is apparently ubiquitous and has significant implications for the flexibility of developmental evolution of both conserved and evolving characters. Current data on the population genetics and molecular mechanisms of DSD illustrate how the details of developmental processes are constantly changing within evolutionary lineages, indicating that developmental systems may possess a great deal of plasticity in their responses to natural selection.

/pdf/developmental-system-drift-and-flexibility-in-evolutionary-2ud8w3w20d.pdf

Developmental system drift and flexibility in evolutionary trajectories

North America and South America have recently been colonized by the Palearctic species Drosophila subobscura. This double colonization offers a rare opportunity for evolutionary studies. Correlations between chromosomal arrangement frequencies and latitude were calculated for the colonizing populations. Signs of these correlations are highly coincident with those found in the Old World. These results provide experimental support for the adaptive value of the chromosomal-inversion polymorphism; historical and other nonadaptive explanations are thus excluded or relegated to a secondary role.

https://www.pnas.org/content/pnas/85/15/5597.full.pdf

Colonization of America by Drosophila subobscura: Experiment in natural populations that supports the adaptive role of chromosomal-inversion polymorphism

Drosophila subobscura is a Palearctic species that has been extensively studied by population and evolutionary geneticists for nearly half a century. In 1978, it appeared in Puerto Montt, Chile; wi...

/pdf/a-grand-experiment-in-evolution-the-drosophila-subobscura-2nuhse5gpq.pdf

A grand experiment in evolution: the Drosophila subobscura colonization of the Americas

In February 1978, in Puerto Montt (Chile) the palearctic species Drosophila subobscura was detected. The expansion of the species in this country has been very rapid, and now it is found over a distance of at least 2000 km North-South. The newly established populations are very flourishing and show a high degree of inversion chromosomal polymorphism. On the basis of the chromosomal arrangements present, an hypothesis can be formulated about the origin and characteristics of the founder group. Possibly, the founders came from Eastern or South Eastern Spain and formed a group of 10 or more individuals. The colonization of D. subobscura in Chile seems to follow the model of expansion of a cosmopolitan species, passively transported by man rather than the more active expansion of colonizers less tied to human activity, envisaged in Carson's models of colonization processes. The high level of chromosomal polymorphism observed in the populations of D. subobscura in Chile, coincides with this interpretation.

Colonization of Drosophila subobscura in Chile I. First population and cytogenetic studies

Drosophila subobscura is a Palearctic species that was first detected in the New World in Puerto Montt (Chile) in February 1978. Since that time, it has spread over a broad area and increased in population density. The South American populations exhibit a high level of chromosomal polymorphism: 20 different arrangements exist, distributed among five chromosomes. Chromosomal arrangement heterozygosity varies from 0.55 to 0.61 in the nine populations examined. Incipient clines in the frequencies of the arrangements are appearing; these clines follow the same latitudinal direction as in the Old World. Wing length significantly decreases with latitude, as it does in Europe. The colonization of South America by D. subobscura appears to be a major natural experiment with outcomes that duplicate the distributional patterns-in chromosomal polymorphism and in wing length- observed in the Old World, thereby strongly supporting the adaptive significance of these patterns. The data show a very rapid effect of natural selection promoting genetic differ- entiation among natural populations.

The colonization of drosophila subobscura in chile. ii. clines in the chromosomal arrangements.

selection on genetic change at individual loci. Proc. Natl. Acad. Sci. USA 75(12):6168-6171. LANDE, R. 1975. The maintenance of genetic variability by mutation in a polygenic character with linked loci. Genet. Res. 26: 221-235. LYNCH, M. 1984. The selective value of alleles underlying polygenic traits. Genetics 108: 1021-1033. MACKAY, T. F. c., R. F. LYMAN, M. S. JACKSON, C. TERZIAN, AND W. G. HILL. 1992. Polygenic mutation in Drosophila melanogaster: Estimates from divergence among inbred strains. Evolution 46:300-316. NAGYLAKI, T. 1992. Introduction to theoretical population genetics. Springer, New York. RENDEL, J. M. 1967. Canalisation and gene control. Academic Press, New York. SCHARLOO, W. 1988. Constraints in selection response. Pp. 125149 in V. Loeschke, ed. Genetic constraints in adaptive evolution. Springer-Verlag, Berlin. SHEARN, A. 1989. The ash-I, ash-2, and trithorax genes of Drosophila melanogaster are functionally related. Genetics 121:517525.

A. Prevosti

Papers

Colonization of America by Drosophila subobscura: Experiment in natural populations that supports the adaptive role of chromosomal-inversion polymorphism

A grand experiment in evolution: the Drosophila subobscura colonization of the Americas

Colonization of Drosophila subobscura in Chile I. First population and cytogenetic studies

The colonization of drosophila subobscura in chile. ii. clines in the chromosomal arrangements.

Temporal changes in chromosomal polymorphism of drosophila subobscura related to climatic changes.