Spermiogenesis and sperm ultrastructure in Cylindrostoma fingalianum (Platyhelminthes,Prolecithophora) with notes on a protozoan (kinetoplastid) symbiont closely associated with allosperm

Summary

The only positive synapomorphy uniting members of the platyhelminth turbellarian taxon, Prolecithophora, is a peculiar membranous system present in much of the shaft of the sperm. This investigation followed the development of this membrane system during spermiogenesis in Cylindrostoma fingalianum and its appearance in the mature sperm. Formation begins with invaginations of the early spermatid shaft outer cell membrane. The invaginations enlarge and the membrane becomes increasingly folded. They appear to be subsequently supplemented with membranous material supplied by an extensive vacuolar system originating from the Golgi apparatus in the main cytoplasmic mass of the spermatid. Throughout development, and in mature sperm, the membranous system forms a part of the outer cell membrane and is also intimately associated with the elongate mitochondrion that lies between the membranous column and the nucleus. The nucleus is highly lobed and the sperm cell lacks flagella or axonemes or the dense bodies found in most other turbellarian taxonomic divisions. A kinetoplastid protozoon present in considerable numbers amongst allosperm is also described.     

Patterns of seasonal and yearly mass variation in West African tropical savannah birds

Birds in the northern hemisphere usually increase mass reserves in response to seasonal low temperatures and shorter day length that increase foraging unpredictability and so starvation risk. In the lowland tropics, relatively low temperatures and short day lengths are absent and so the risk of starvation may be reduced, leading to much smaller seasonal effects on mass. Nevertheless, other factors such as high temperatures and water and food availability may vary greatly between tropical wet and dry seasons, leading to variable starvation risk and seasonal mass effects. Using data collected from 47 species of birds caught over a 10‐year period in a tropical savannah region in West Africa we tested for seasonal variation in mass in response to a predictable, strongly seasonal tropical climate. Many species (91%) showed seasonal variation in mass, and this was often in a clear annual pattern that was constant across the years. Many species (89%) varied their mass in response to seasonally predictable rainfall. Annual variation in mass was also important (45% of species). Relatively few species (13%) had a seasonal pattern of mass variation that varied between years. Feeding guild or migratory status was not found to affect seasonal or annual mass variation. Seasonal mass change was on average 8.1% across the 21 species with a very large sample size and was comparable with both northern and southern temperate species. Our study showed that biologically significant consistent seasonal mass variation is common in tropical savannah bird species, and this is most likely in response to changing resource availability brought about by seasonal rainfall and the interrupted foraging response due to the constraints of breeding.