Question

The sailfin molly, Poecilia latipinna, is an interesting freshwater fish possessing internal fertilization. In this species, males either court females or attempt forced copulations without courting. Larger males court more frequently than smaller males whereas the latter attempt more forced copulations. Variation in male size appears to be strongly influenced by alleles at a single genetic locus on the Y chromosome. Describe simple genetic crosses and an experiment in which you could determine whether the two male behaviors represent either (i) size-dependent adaptive strategies without an underlying genetic basis, or (ii) genetically-based alternate male reproductive strategies.

Answer 1

Since variation in male size is found to be strongly affected by alleles at a particular single genetic locus on the Y chromosome, the size-dependent adaptive strategies seem to be utilized by the sailfin molly. If the male has inherited an allele that confers large size, then it will have large body size. If the male has not inherited that particular allele, then it will have small body size. As an adaptive strategy, large males court more frequently whereas small males attempt forced copulations. Since, the alleles located at a single genetic locus on Y chromosome primarily affects the male size and not the copulation habbits, so the copulation behaviour exhibited by this freshwater fish can considered to be merely an adaptive strategy.