Rodent louse diversity,phylogeny, and cospeciation in the Manu Biosphere Reserve,Peru

We investigated the diversity, cophylogenetic relationships, and biogeography of hoplopleurid sucking lice (Phthiraptera: Anoplura) parasitizing rodents (Muridae: Sigmodontinae) in the Manu National Park and Biosphere Reserve. Our morphological and molecular studies reveal that 15 distinct louse species parasitize 19 rodent species. Three of these louse species are new to science, and all but two of the host associations were previously unknown. We find that hoplopleurid lice in South America parasitize multiple host species across a large geographic area, and that Peru represents a new geographic locality for almost all the louse species collected in the present study. Phylogenetic analyses of mitochondrial and nuclear data reveal that the louse family Hoplopleuridae and the genera Hoplopleura and Pterophthirus are not monophyletic, and lice do not appear to group by host tribe, collecting locality, or collection elevation. The lack of monophyly for these apparently natural groups (taxonomic, locality, and elevation) indicates that host switching with or without parasite speciation may be prevalent among hoplopleurid lice. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 598–610.     

Endogenous Gibberellins and Growth of Tobacco Callus Cultures

Tobacco callus grown under a range of conditions for different lengths of time contained various levels of gibberellin-like substances. Culture conditions, viz: light versus darkness and the quantity of cytokinin in the medium, affected the amount of gibberellins found in the tissue. These culture conditions were also important in controlling growth rate of the callus and modified the ability of the tissue to respond to exogenous gibberellins. Furthermore, substances which are known to inhibit gibberellin biosynthesis and also thought to block gibberellin action in some cases, were found to reduce the rate of growth. These data support the idea that endogenous gibberellins may be important in the control of the normal growth of tobacco cells in culture.     

Lymphocyte Trapping in Tolerant Mice

THE precise nature of the cellular defects involved in a state of immunological unresponsiveness remains to be elucidated¹. As one of the earliest events in the initiation of humoral immune responses is the recruitment of peripheral lymphocytes^6–11, we have investigated the kinetics of recruitment in tolerant animals.     

Bite force in vertebrates: opportunities and caveats for use of a nonpareil whole-animal performance measure

Measurements of whole-organism performance traits have been useful in studies of adaptation and phenotype–environment correlations. Bite force capacities may be tightly linked to both the type and magnitude of the ecological challenges of food acquisition, mate acquisition, and antipredation in vertebrates. In the present study, we present technical details on bite meters and on measuring bite forces. The ability to take reliable measurements depends on specific features of the measuring device and on where in the mouth the bite is applied. Using both previously available and original data, we demonstrate several ecologically and evolutionarily relevant features of bite force measurements. First, maximal bite forces are repeatable among individuals across all vertebrates studied to date. Second, in ectotherms such as lizards, maximal bite forces are affected by body temperature and motivational states. Third, bite forces are strongly correlated with head size and shape. Fourth, bite forces correlate with features of prey of vertebrates. Finally, bite forces are linked to male dominance and correlated with social-display structures. Thus, bite force performance measures can be used as 'traits', and thus be used in integrative studies at multiple levels of organismal biology. Accordingly, bite force data will help our understanding of the functions, capacities, and evolution of jaw–cranial musculoskeletal systems. Moreover, a plethora of opportunities exist for the use of bite force measurements, and if methods are carefully applied, several levels of organismal and ecological organization can be integrated to aid our understanding of the ecology and evolution of vertebrate taxa.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 709–720.     

Grasshopper egg mortality mediated by oviposition tactics and fire intensity

Abstract.  1. It is commonly assumed that arthropod species living or hibernating in the soil would not be affected by grassland fires, even though burning results in elevated surface and below-ground soil temperatures. The importance of elevated below-ground soil temperatures during fires on the survival of grasshopper eggs had not been examined.
2. The effects of simulated autumn grassland fires of varying intensities on below-ground egg mortality were examined with grasshopper species laying shallow egg pods ( Ageneotettix deorum ) and deeper egg pods ( Melanoplus sanguinipes ) to test the hypothesis that exposure to heat during fires was the mechanism responsible for population reductions in A. deorum following fire.
3. Species-specific oviposition characteristics mediated the effects of fire intensity on below-ground egg mortality. The results indicate that fires occurring in areas with at least 3100 kg ha⁻¹ standing crop biomass would be expected to significantly reduce populations of A. deorum , but not M. sanguinipes . No A. deorum eggs hatched in 12 of the 14 oviposition containers subjected to simulated fires approximating a standing crop biomass of 4500 kg ha⁻¹. This is the first study to link field observations of rangeland insect populations following fire to mechanisms related to below-ground egg mortality.     

An African twin to the Brazilian Calamopleurus (Actinopterygii: Amiidae)

A new species of amiid fish, Calamopleurus africanus sp. nov., is described on the basis of fragmentary material from ?Albian Kem Kem beds of southern Morocco. The new species shows several derived characters of the genus Calamopleurus such as ossified dermopterotic ribs, an inferred loose association between the dermosphenotic and the skull roof, a gular plate with a scalloped posterior margin, and a hyomandibular with a very long posterior (opercular) process. It differs from the type species in the proportions of the frontals, supramaxilla and gular. The distribution of Calamopleurus and some other Lower Cretaceous fishes is discussed in the context of the presumed adjacency of west Africa and eastern Brazil during much of the Mesozoic.     

Sex Determination in Reptiles: An Update

Sex determination and sex differentiation are two separate butrelated phenomena. Sex differentiation is a programmed cascadeof events in which the indifferent gonad develops as a testisor an ovary with the appropriate urogenital and secondary sexcharacters. Sex determination is the event that sets this cascadein motion. In placental mammals, there is good evidence thatsex is determined by a gene on the Y chromosome (SRY) that initiatestestis formation. In the absence of SRY an ovary develops. Thereare, however, examples of placental mammal that develop as normalmales with no detectable SRY. In reptiles, sex differentiationappears to be similar to mammals (i.e., the same genes and hormonesact ina similar manner), but sex determination is clearly verydifferent. Ovarian differentiation in placental mammals canoccur in the absence of estrogen or an estrogen receptor. Ovariandifferentiation in reptiles requires the presence of estrogen.In the absence of estrogen a testis develops. In TSD reptiles,embryos will develop as females when treated with estrogen evenif eggs are incubated at male-inducing temperatures, and conversely,will develop as males when estrogen synthesis is blocked ineggs incubated at female-inducing temperatures. A number ofother genes have also been shown to be important in mammaliansex determination. One of these genes, Sox9, which is expressedin differentiating mouse testis, has recently been found tobe expressed in embryonic reptile testis. Other genes that appearto be common to both mammals and reptiles in the sex determiningcascade are SF- 1, MIH, and possibly DAX-1. Current researchis now focused on how the gene that produces the enzyme necessaryfor estrogen synthesis (aromatase) is regulated in the embryosof reptiles with genetic or environmental sex determination.Controversial issues in reptilian sex determination are 1) therole of the brain in gonadal sex determination, and 2) the roleof steroid hormones in the yolk prior to sex determination