In comparing two nearby lakes, you find four distinct fish species, with two spe

Question

In comparing two nearby lakes, you find four distinct fish species, with two species occurring in each lake. Each lake has its own “showy” species with large fins (A and B), and each lake also has its own “cryptic” species (C and D).

You are curious about how they may have evolved. You form two hypotheses about the evolution of these fish and decide to test them by constructing a phylogeny.

Below each hypothesis, draw the phylogeny that you would expect to find if that hypothesis is true, and explain your reasoning.

Hypothesis 1: The two lakes were originally a single large lake that was divided in two which led to allopatric speciation

Hypothesis 2: The “showy” and “cryptic” species are examples of convergent evolution to similar ecological pressures. Speciation occurred sympatrically within each of the two lakes.

Explanation / Answer

Hypothesis 1: Ans:

Allopatric speciation – The evolution of reproductive isolation between populations that are geographically separated.

Because of the unreliability of inferences of geographical ranges in the past, interspecific phylogenetic approaches
are unlikely to add much to the debate over sympatric versus ALLOPATRIC SPECIATION.Although phylogenetic studies have suggested surprisingly high rates of sympatric speciation, allopatric speciation is still usually identified as the predominant mode in such studies.Most interspecific phylogenetic approaches to the geography of speciation work by examining the distribution of sister taxa: for example, if they are sympatric, then speciation is inferred to have been sympatric and if they are allopatric, speciation is inferred to have been allopatric.

Hypothesis 2:Ans:phylogenetic approaches have been proposed to determine the geographical mode of speciation. If reliable, these methods not only provide a means of settling the debate about the geography of speciation, but also indicate that sympatric speciation is surprisingly common and that peripatric speciation is relatively rare The interspecific phylogenies are unable to test alternative hypotheses concerning the geography of speciation rigorously because of the lability of geographical ranges and the lack of correlation between the role of adaptive processes and geographical mode of speciation.

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