Evolution (Biology)

Larval release by adult fiddler crabs occurs during the ebbing tides, but its timing
relative to the day-night and tidal amplitude cycles depends upon tidal form (e.g., shows
phenotypical plasticity). Crabs (Uca thayeri) from Florida's East Coast are exposed to
semidiurnal tides and release their larvae at night, whereas crabs from Florida's West
Coast exposed to mixed tides release their larvae during the afternoon. The purpose of
this study was to determine whether the larvae could hatch at times other than those
correlated with the tidal form at their location. Clusters of eggs at similar stages of
development, 24-72 h in advance of release, were reciprocally transferred between
females from each coast. Release ofboth the transferred larvae and maternal clutch
occurred synchronously, and at the time dictated by the female's tidal regime. These
results suggest that larvae are phenotypically plastic with respect to hatching time and
can either delay (West coast) or advance (East coast) their response to release signals
from females.

A phylogeny of Mexican Ambystoma salamanders was constructed using
larval morphology. Characters were scored for 19 ambystomatid species from
Mexico and North America Twenty-five continuous characters came from
external measurements of cranial and branchial features and ratios of
measurements. Twenty-six categorical characters were scored from internal and
external larval, branchial, and cranial features, as well as overall color and adult
life history. Cladograms constructed from individual character matrices lack
major resolution beyond individual species level. The consensus cladogram did
not resolve the majority of species, and was similar to consensus results from
previous cladistic analysis based on molecular characters. Convergent
morphology is evident in characters of geographically distant members of the
clade. However, species determination was possible for all examined taxa.
Neoteny is widespread in the A. tigrinum complex and, as an isolating
mechanism, may be the main driver of speciation in the complex.

The hard clam aquaculture industry has largely been limited to the cultivation of the species Mercenaria mercenaria. Two Florida native species of clam, Noetia ponderosa and Anadara ovalis, commonly known as "Ark clams" are being studied for their viability as potential aquaculture species. Early development of the blood ark, Anadara ovalis (Bruguiere, 1789), and the ponderous ark, Noetia ponderosa (Say, 1822) was analyzed with an emphasis on the processes of meiotic maturation and early embryogenesis through gastrulation, using light and fluorescence microscopy. Both A. ovalis and N. ponderosa oocytes were released at the metaphase I stage of meiosis and shared similar schedules of early development through initial veliger stage. Differences in the timing of development between species were negligible. In addition, the behavior and developmental timeline of the ark clams was very similar to that of Mercenaria mercenaria , which also reaches the D-shaped veliger stage in less than 24 hours.

The human prefrontal cortex (PFC) is associated with complex cognitive behaviors such as planning for the future, memory for serial order, social information processing and language. Understanding how the PFC has changed through time is central to the study of human neural evolution. Here we investigate the expansion of the PFC by measuring relative surface area of the PFC in Pan troglodytes and Homo sapiens. Magnetic resonance images (MRI's) from 8 preserved chimpanzee brains (3 male and 5 female adults) were segmented and measured. The results of this study indicate that there are gross anatomical differences between the chimpanzee and human prefrontal cortex beyond absolute size. The lower surface area to volume ratio in PFC of the chimpanzee when compared to a human indicates less gyral white matter in this region and thus, less associative connectivity. This anatomical evidence of a difference corresponds with the lesser cognitive complexity observed in chimpanzees.