This study is an investigation of processes of evolution in planktonic foraminifera using stable isotopic analysis. In the absence of obvious barriers to gene flow such as land masses (e.g. Isthmus of Panama) or major oceanographic boundaries (e.g. Polar Front and Tasman Front), how does evolution proceed in large pandemic populations in which gene flow is readily maintained over great distances? How do chronospecies gradually evolve within one biographic province? Most models predict that evolutionary change in the deep-dwelling planktonic foraminifera occurs through segregation within the water column during times of well developed depth stratification. In broader terms, the globorotalid morphology is believed to have evolved iteratively in association with adaptation to increasing water depths. However, almost no data have been have been generated to test such hypotheses. We will isotopically analyze morphometrically-defined Late Miocene to Recent species of the Globoratalia (Globoconella) clade in sedimentary sequences that form a meridional transect in the southwest Pacific. A time-series strategy will be employed focusing upon those stratigraphic intervals in which there is overlap in the ranges of ancestor and descendant species. Some of the questions we will address include: Do ancestor and descendant species exhibit consistent differences in isotopic values, suggesting vertical or seasonal segregation in the water column? Are there isotopic trends within this clade, suggesting progressive habitation of cooler or warmer waters, either vertically or seasonally? Are the isotopic trends associated with paleoceanographic changes? Are the isotopic trends associated with specific morphological characters? Do ancestor and descendant species living in different water masses, some within and some peripheral to the main biogeographic range of the clade, exhibit similar differences in isotopic values and similar paleoceanographic and morphological associations? How do the stable isotopic results from the Globorotalia (Globoconella) clade compare with those from another deep-dwelling planktonic foraminiferal clade that, in part, exhibits similar morphologic characteristics: - the Globorotalia (Truncorotalia) clade?
