On the Significance of Variation in a Warm Water Cosmopolitan Species, Nominally Ceratoscopelus Warmingii (Pisces, Myctophidae)
Abstract:The lanternfish Ceratoscopelus townsendi-warmingii complex is currently recognized as containing two species, C. townsendi, a N.E. Pacific endemic, and C. warmingii, a subtropical-tropical cosmopolite. A comparison of specimens from around a N. Atlantic frontal area, the Azores front (ca. 33°N:32°W), shows that within the area two distinct forms of nominal C. warmingii exist, their separating geographic boundaries more or less coinciding with the frontal boundary. Although considerable variation, particularly that in the number and disposition of luminescent structures, is known to occur within nominal C. warmingii and to show, in the Atlantic and Indian oceans, some geographic correlations, the situation is more complex than previously appreciated. Comparison of nominal C. warmingii characters, including larval ones, between specimens from different areas of its geographic range with those of C. townsendi leads to the conclusion that the C. townsendi-warmingii complex should be regarded as comprising a single species, C. townsendi, containing a number of distinct and geographically separated populations. At least 6 variants are distinguishable, represented globally by at least 13 discrete populations, as 6 Atlantic, 3 Indian Ocean and 4 Pacific ones. Boundaries between populations appear to be relatively sharp and such evidence as exists suggests that interpopulation variations are the result of restrictions imposed in some cases by hydrographic barriers and in others by differences in breeding timetables.
In reality, while some of the previously recognized cosmopolitan species may comprise a species-complex, others, including C. townsendi, represent a single species composed of a number of distinct and geographically separated populations that show distributional concordance with known species assemblages. Insights into how such intraspecific populations arose and are maintained are important in understanding the processes involved in the evolution of communities. For many broadly distributed species, gene flow between intraspecific populations may be rather weak and the population characters themselves an expression of genetic divergence. The zoogeographic implications of this are great but, in particular, appreciation of adaptations across boundary areas will provide valuable insights into community evolution.
Document Type: Research Article
Publication date: 1988-01-01
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