Biology Reference
In-Depth Information
loux et al. 2002).The
aegypti
form appears to have arisen in North Africa
by adaptation of the mosquito to breeding in water storage vessels. This
form was spread worldwide in tropical and subtropical areas by commerce
between the fifteenth and nineteenth centuries.The forest form,
formosus
,
has also been introduced to some islands in the Indian Ocean.
Aedes aegypti aegypti
itself shows genetic differentiation in different
tropical regions. Populations in South America and Southeast Asia are
genetically similar and are the most efficient vectors of the dengue virus
(Failloux et al. 2002). South American mosquitoes, however, are effective
vectors of the yellow fever virus, whereas Southeast Asian mosquitoes are
not. Subspecies
aegypti
in Polynesia is somewhat distinct from the South
American and Asian forms of the subspecies, perhaps as the result of a
genetic bottleneck at the time of introduction. Subspecies
formosus
on La
Réunion Island in the Indian Ocean also differs from populations in
African forest areas and is a more efficient vector of dengue than African
forest populations.This difference may also have arisen by a founder effect
or as an accidental consequence of mosquito control efforts from 1949 to
1953.
Rapid Evolutionary Adaptation by Aquatic
Ve r tebrate Predators
Adaptations for use of prey of a certain size range are common in aquatic
vertebrate predators, and many examples of differentiation between sexes
or competitor species have been documented (Smith and Skúlason 1996).
Although some such differences are the result of phenotypic plasticity,
many are genetically based.The genetic basis is often quite simple, at times
the result of a single gene. Situations in which rapid evolution of adapta-
tions for altered prey use occurs often involve the invasion of new regions
or habitats.
Freshwater fish at northern latitudes in the northern hemisphere pres-
ent many examples of such divergent evolution, much of which has
occurred since retreat of Pleistocene continental glaciers about 15,000 yr
ago. These most recent examples are probably replicates of changes fol-
lowing the 20 or so phases of glaciation that occurred over the past 2 mil-
lion yr. In this most recent postglacial era, colonization of new, biotically
impoverished aquatic environments from freshwater refugia or from the
ocean has offered many ecological opportunities and has led to some
remarkable patterns of adaptive radiation (Robinson and Schluter 2000).
Many of these patterns are replicated in different lake and river systems.
