Courtship Sequences and Ethological Isolation in Two Species of Sunfish (Lepomis Spp) and Their Hybrids

Publisher Website
Google Scholar
Abstract
The role of courtship behaviour in ethological isolation was studied by analysing courtship sequences between different crosses of pumpkinseed (Lepomis gibbosus), bluegill (L. macrochirus), and their hybrid sunfish. Crosses were established in large laboratory tanks, under an artificially advanced photoperiod and temperature regime, and in outside pools. Male-female interactions were filmed and videotaped. In the field, underwater films of naturally occurring courtship and spawning were taken. A behavioural repertoire was described and the data converted to pairs of male and female acts (dyads). Two contexts were distinguished (spawn and nonspawn) depending on whether courtship led to spawning or not. Several methods of analysis were used. Multidimensional contingency table analysis with factors of preceding act, following act, and cross, enabled examination of the dependence of the response of any individual (sex or species) upon the species of partner. Multidimensional Scaling of the crosses, based on a chi-square measure of overall dissimilarity for each context, revealed the relative proximities among the different interspecific and hybrid crosses and the parentals. The results generally agreed well with those produced by a clustering technique. The conclusions are: (1) The differences between the courtship and spawning behaviour of the parentals are evidence for a behavioural isolating mechanism. (2) Interspecific and hybrid crosses tend to be intermediate to parentals. (3) Courting and spawning behaviour is different in the laboratory and field environments. (4) Hybrids likely originate from crosses of male bluegills and female pumpkinseeds. The role of courtship behaviour in ethological isolation was studied by analysing courtship sequences between different crosses of pumpkinseed (Lepomis gibbosus), bluegill (L. macrochirus), and their hybrid sunfish. Crosses were established in large laboratory tanks, under an artificially advanced photoperiod and temperature regime, and in outside pools. Male-female interactions were filmed and videotaped. In the field, underwater films of naturally occurring courtship and spawning were taken. A behavioural repertoire was described and the data converted to pairs of male and female acts (dyads). Two contexts were distinguished (spawn and nonspawn) depending on whether courtship led to spawning or not. Several methods of analysis were used. Multidimensional contingency table analysis with factors of preceding act, following act, and cross, enabled examination of the dependence of the response of any individual (sex or species) upon the species of partner. Multidimensional Scaling of the crosses, based on a chi-square measure of overall dissimilarity for each context, revealed the relative proximities among the different interspecific and hybrid crosses and the parentals. The results generally agreed well with those produced by a clustering technique. The conclusions are: (1) The differences between the courtship and spawning behaviour of the parentals are evidence for a behavioural isolating mechanism. (2) Interspecific and hybrid crosses tend to be intermediate to parentals. (3) Courting and spawning behaviour is different in the laboratory and field environments. (4) Hybrids likely originate from crosses of male bluegills and female pumpkinseeds.