Latitudinal Variation in Breeding Patterns

One goal of biological studies is to find generalizations about organisms that can be used to explain patterns observed in nature. These generalizations also help to predict how organisms will respond under particular environmental situations, present and future. Part of my work on reproduction in shrimps has been to describe the temporal patterns of breeding in hopes of determining the causal factors of such patterns. Especially, some of my studies have examined the seasonality of reproduction: does reproduction occur all year (continuous) or just in a particular period of the year (seasonal). Tropical species of caridean shrimps were found to breed continuously (see Bauer, 1989a, 1992a). In the seagrass shrimps of the genus Thor, species of living in tropical areas reproduce throughout the year while those from higher (warm-temperate) latitudes show seasonal patterns (see Bauer, 1992b; Bauer and VanHoy, 1996).

Similarly, a comparison among species of the penaeoid shrimp genus Sicyonia shows that tropical species breed continuously, subtropical species have a lengthy but seasonal breeding season, and a cool temperate species showed breeding confined to even a more restricted period during the year (see Bauer, 1992a).   The subtropical Gulf of Mexico penaeids Rimapenaeus similis and R. constrictus show somewhat extended but still seasonal breeding patterns (Bauer and Lin, 1994).

The studies cited above are based on samples of shrimps collected throughout the year. Measurements are taken on their breeding characteristics, especially those of females (degree of ovarian development and, in caridean shrimps, presence and degree of development of attached embryos).

I have tried to relate breeding patterns to factors of the environment which may have caused them to evolve (selective pressures). These include the seasonality of production of larval food supplies and the intensity of predation pressure in the environment. Although it is sometimes hard work to describe the patterns of breeding, the observations needed to test hypotheses about factors explaining these patterns is even more difficult. Lots of work for an interested marine biologist to do! Look also for the very good work on this theme by a group of Brazilian investigators working in southeaster Brazil (Adilson Fransozo, Maria Lucia Fransozo, Antonio Castillo (UNESP Botucatu), Rogerio Costa UNESP Bauru), Fernando Mantelatto (USP, Ribeiro Preto) and their students.

References Cited

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