Roger Lubbock

Group sex ratio and sex reversal

Abstract In hermaphroditic fishes, the initiation of sex reversal by male removal explains the replacement of lost males but does not explain how the number of males in a group may increase. Since numerous species apparently cannot produce primary males, a second means of initiating sex reversal must exist. In the present study we formulate a model which suggests the existence of an additional mechanism governing sex change: as soon as the ratio of adult females to males within a group exceeds a certain threshold value, a female changes sex even though no male has been removed. This process is inferred from comparison of data collected in the Red Sea and the western Indian Ocean with the models predictions concerning size at sex reversal and the sex ratio of groups. The results suggest how several ecological factors may influence the occurrence rate of sex reversal and the development and growth of social groups.

Marine zoogeography of St Paul's Rocks

The zoogeographical relationships of the shallow water marine fauna of St Pauls Rocks (equatorial Atlantic) are examined with respect to ocean current patterns. Of seventy-seven benthic species considered, 46% are amphi-Atlantic, 14% occur at the central Atlantic islands of Ascension and/or St Helena as well as in either the eastern or western Atlantic, and 5% are endemic to the Rocks. Of the remaining twenty-seven species, 74% are shared only with the western Atlantic, 15% only with Ascension/St Helena, and 11% only with the eastern Atlantic. We deduce that the primary route of immigration for shallow water benthic species has been from Brazil, via the Atlantic Equa- torial Undercurrent. Some input from Ascension Island and West Africa by means of the South Equatorial Current is also indicated. The zoogeographical composition of the St Pauls fauna is discussed in relation to current velocities and larval lifetimes. We conclude that St Pauls is essentially an impoverished

Mucus antigenicity in sea anemones and corals

The antigenicities of external mucus from the sea anemones Stoichactis haddoni, Radianthus ritteri and Gyrostoma hertwigi and from the coral Trachyphyllia geoffroyi were compared. Marked differences were found between species but not within species. The differences suggested that mucus composition might be species specific, and hence that it might be one of the factors used by sea anemones and corals in the recognition of foreign anthozoan species.

Fishes of the family Pseudochromidae (Perciformes) in the central Indian Ocean

Summary A brief review of literature on central Indian Ocean Pseudochromidae is provided, followed by a key to central Indian Ocean species. Two new species, Chlidichthys inornatus and Pseudochromis dilectus, are described.

Two distinctive new Australasian Pseudochromis (Teleostei: Perciformes)

Summary Two new Australasian species of Pseudochromis are described. P. flammicauda sp. nov. is characterized by a yellow head, dark brownish grey body and bright red caudal fin. P. paranox sp. nov. is characterized by head, body and all fins being jet black; P. paranox appears to be a mimic of the pomacanthid Centropyge nox.