Seasonal patterns of reproductive activities among deep-sea benthic copepod species in the bathyal Sagami Bay, central Japan

Little is known about the life histories of the deep-sea metazoan meiobenthos. At a bathyal site (depth 1430 m) in Sagami Bay, central Japan, temporal changes in abundance and reproductive activity of deep-sea benthic copepods were investigated for eight abundant species that composed about 50% of total individuals, based on samples collected before fresh organic matter increased in the sediment (December 1996 and 1997), 1 month thereafter (June 1997 and May 1998), and a few months after the event (August 1997 and 1998). Densities of adults of these species fluctuated among samples (the total abundance was 5–30 individuals/10 cm²), but did not show any seasonal trend. Strong evidence for competitive relationships among species could not be detected, and there was no significant negative correlation in abundance between any species pair. The percentage of ovigerous females among total adult females of Schizopera sp. 1 differed significantly by month. Furthermore, the adult sex ratio of the species appeared to fluctuate temporally. These suggest a temporal change in reproductive activity and synchronized growth of Schizopera sp. 1. There was no temporal trend, however, in any parameter for the other species. Mean egg number per brood and egg diameter differed among species, but did not change seasonally in any species. Our study suggests the rarity of seasonal breeding species among the deep-sea benthic copepods, one of the major metazoan meiofaunal groups, as well as among other macro-megafaunal metazoans.     

Brain Evolution: Mammals,Primates, Chimpanzees,and Humans

Though many modern techniques are available for studying brains, they are difficult to use in evolutionary contexts that require examination of large numbers of specimens and species, and all major parts of the brain. Thus, evolutionary studies of many species and of whole brains still tend to be based upon simpler data such as sizes of brains and brain components. Such investigations, carried out over many decades, have usually employed univariate and bivariate analyses, though a few investigators used early multivariate methods. In mammals, these studies generally show the primacy of the relationship between brain and brain-part sizes with overall body size. More recent multivariate applications have confirmed this (Finlay, B. L., and Darlington, R. B. (1995). Science 268: 1578–1584) and some have also separated the highest level phylogenetic groups: strepsirrhines and haplorrhines (Barton, R. A., and Harvey, P. H. (2000). Nature 405: 1055–1058). Both findings were, in fact, evident in earlier multivariate studies (Holloway, R. L. (1979). In Hahn, M. E., Jensen C., and Dudek, B. C. (eds.), Development and Evolution of Brain Size: Behavioral Implications, Academic Press, New York, pp. 59–88; Sacher, G. A. (1970). In Noback, C. R., and Montagna, W. (eds.), The Primate Brain: Advances in Primatology. Vol. 1, Appleton-Century-Crofts, Educational Division, Meredith Corporation, New York, pp. 245–287). However, new studies employing proportional data aimed at conveying input/output relationships between brain components show further groupings of species that share convergences in lifestyles (de Winter, W., and Oxnard, C. E. (2001). Nature 409: 710–714). The convergences are brought about by combinations of brain variables that seem to be associated with brain functions implied by the specific lifestyles. Our most recent results demonstrate that chimpanzees and humans are especially different from one another, and the difference is not due to size alone. Part of this difference is merely a continuation, from chimpanzees towards humans, of a trend already present across all other primates that relates mainly to neocortical increase. But several other large and independent differences are not in the direction of the overall primate trend, but are differences of humans from all other mammals examined including all nonhuman primates. The combinations of brain variables associated with the latter differences are not related simply to enhancement of the neocortex, but seem to reflect other internal relationships. The overall separation of humans and chimpanzees is so large that it goes far beyond the conventional 98.6% commonality in their DNAs. It fits better with more recent molecular, developmental and evolutionary studies implying a considerably greater difference between chimpanzees and humans than usually recognized.