Search

Earth's economic woes haunt the first lunar colony in a fictional near future

Prey material, which was collected from beneath the nests of two pairs of crowned hawk-eagles (Stephanoaetus coronatus) in the Ngogo study area, Kibale National Park, Uganda, was analyzed to identify the taphonomic features diagnostic of eagle predation. Material from a recent three-year collection interval was compared to an earlier three-year collection subsample to determine signal consistency over time. The bulk of the assemblage is comprised of cercopithecoid monkey remains, reflecting the taxonomic composition of the Ngogo area. Taxonomic composition of the assemblage remains highly consistent over the collection period. Bone survivability and fragmentation profiles, as well as damage patterns, also were investigated. Crowned hawk-eagles inflict much less damage to prey skeletons than do mammalian carnivores. Crania, scapulae, and hindlimb elements are most likely to survive predation by crowned hawk-eagles and to be concentrated at nest sites, but these elements (especially crania) show ag...

In this study, I investigate body-form variability in the trophically polymorphic Cuatro Cienegas cichlid, Cichlasoma minckleyi. I use geometric morphometrics to assess and compare size, shape, and allometric patterns within and between dental morphs (distinguished by differences in pharyngeal bones and papilliform or molariform dentitions). I find that dental morphs do not differ significantly in size, shape, or allometric slopes, but do differ in allometric intercepts; thus, dental morphs exhibit different patterns of body-form variability. Within each morph, body-form varies between more fusiform 'piscivores' and deeper-bodied dietary generalists. However, papilliform individuals show a continuous distribution of body-forms, whereas molariform individuals exhibit a discontinuity. I compare results from geometric analyses with those from a traditional (distance-based) morphometric analysis, finding that geometric techniques more clearly recognize discontinuities in shape. Finally, I suggest explanations for observed differences in body-form variability between dental morphs, concluding that the best explanation hinges on the relative importance of genetic and environmental factors in influencing body-form.

The endemic cichlids of the Cuatro Cienegas Basin, Coahuila, Mexico are currently grouped in a single polymorphic species, Cichlasoma minckleyi. Two morphs of C. minckleyi were distinguished largely by features of the trophic apparatus, especially the pharyngeal dentition. Variation in body shape, based upon analysis of a set of linear measures, was continuous and did not allow recognition of discrete morphs. Individuals raised in the laboratory on several different diets indicated that trophic morphology had an important genetic component. Individuals raised in the laboratory, however, did not differentiate to the degree seen in comparably sized individuals collected at Cuatro Cienegas. This may be because snails used as food in the experiments were not as hard as endemic snails and indicated that some aspects of trophic morphology were also dependent upon environmental cues.

Most osteichthyans continuously replace their teeth throughout their lifetimes. Replacement teeth may develop in the soft tissue outside the bone to which they will attach (“extraosseous”) or in sockets within the bone (“intraosseous”) beneath their functional predecessor. This paper presents a systematic documentation of the position of developing replacement teeth in teleost fishes, based upon a literature review and examination of modern skeletal material. Plotting the distribution of this character on a cladogram of teleost phylogeny indicates that extraosseous development of replacement teeth is plesiomorphic. Intraosseous development, the derived state, has evolved in at least three clades: in branchial and palatal dentitions of the elopiform Albula; in oral dentitions of several characiforms; and in oral and/or pharyngeal dentitions of various acanthopterygians, especially many perciforms. Two interrelated changes are necessary for the evolution of this derived state: replacement teeth mus...

The fossil record indicates that cypriniform fishes, a group including the zebrafish, lost oral teeth over 50 million years ago. Despite subsequent diversification of feeding modes, no cypriniform has regained oral teeth,suggesting the zebrafish as a model for studying the developmental genetic basis of evolutionary constraint. To investigate the mechanism of cypriniform tooth loss, we compared the oral expression of seven genes whose mammalian orthologs are involved in tooth initiation in the zebrafish and the Mexican tetra, Astyanax mexicanus, a related species retaining oral teeth. The most significant difference we found was an absence in zebrafish oral epithelium of expression of dlx2a and dlx2b, transcription factors that are expressed in early Astyanax odontogenic epithelium. Analysis of orthologous genes in the Japanese medaka (Oryzias latipes) and a catfish (Synodontis multipunctatus) suggests that expression was lost in cypriniforms, rather than gained in Astyanax. Treatment of Astyanax with an inhibitor of Fibroblast growth factor(Fgf) signaling produced a partial phenocopy of the zebrafish oral region, in that oral teeth, and expression of dlx2a and dlx2b, were lost, whereas shh and pitx2, genes whose expression is present in zebrafish oral epithelium, were unaffected. We hypothesize that a loss of Fgf signaling to oral epithelium was associated with cypriniform tooth loss.

Teleost fishes display a remarkable diversity of adult dentitions; this diversity is all the more remarkable in light of the uniformity of first-generation dentitions. Few studies have quantitatively documented the transition between generalized first-generation dentitions and specialized adult dentitions in teleosts. We investigated this transition in the Mexican tetra, Astyanax mexicanus (Characidae), by measuring aspects of the dentition in an ontogenetic series of individuals from embryos to 160 days old, in addition to adults of unknown age. The first-generation dentition and its immediate successors consist of small, unicuspid teeth that develop extraosseously. Multicuspid teeth first appear during the second tooth replacement event, and are derived from single tooth germs, rather than from the fusion of multiple conical tooth germs. We document that the transition from unicuspid to multicuspid teeth corresponds to a change in the location of developing tooth germs (from extraosseous to intraosseous) and in patterns of tooth replacement (from haphazard to simultaneous within a jaw quadrant). In addition, while the size of the largest teeth scales with positive allometry to fish size, the transition to multicuspid teeth is accompanied by an exceptionally large increase in tooth size. (c) 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 145, 523-538.

Dental polymorphism in teleost fishes often involves production of a robust dentition, or “molarization”, in one morph. The lower pharyngeals of a sample of wild-caught individuals of the polymorphic Cuatro Cienegas cichlid, Cichlasoma minckleyi (Kornfield and Taylor) (Proc. Biol. Soc. Wash. 96 (1983) 253), were measured to investigate morphological changes associated with molarization. Principal components analysis demonstrates that dental variability in this species increases in larger fish, and that only the molariform morph contributes to this increase. Reduced major axis regression analyses between pairs of variables indicate that the papilliform morph increases both tooth measures and numbers, whereas the molariform morph maintains a relatively constant number of teeth as it produces teeth of progressively larger size. In the papilliform morph, negative allometric scaling between tooth size and dentigerous area is compensated for by addition of teeth. Tooth size variables are isometric in the molariform morph, and tooth numbers are nearly static. These results are consistent with those reported for other polymorphic cichlid species. Further study is required to elucidate the mechanisms whereby tooth form in polyphyodont species may respond to environmental factors (like food hardness), but possibilities include direct mechanical influences or transmission of signals via nerves to developing replacement teeth.

This study provides a taphonomic analysis of prey accumulations of crowned hawk-eagles (Stephanoaetus coronatus) from Ngogo, Kibale National Park, Uganda, collected over 37 months from below nests of two eagle pairs. Crowned hawk-eagles are powerful predators capable of killing animals much larger than themselves, and are significant predators of cercopithecoid monkeys in forest habitats throughout sub-Saharan Africa. At Ngogo, 81% of the individuals in the kill sample are monkeys. Redtail monkeys (Cercopithecus ascanius) are particularly well represented in the sample, making up 66% of monkeys identified to species. Despite an impressive killing apparatus, crowned hawk-eagles are fastidious eaters that inflict far less damage to bone than mammalian predators. Examination of skeletal material from the Ngogo kill sample reveals that crania, hindlimb elements, and scapulae survive predation better than do other bones. Crania of adults are typically complete and accompanied by mandibles, while crania of young individuals are usually dissociated from mandibles and lack basicrania and faces. Long bones are often whole or show minimal damage. Thin bones, such as crania and innominates, are marked by numerous nicks, punctures, and “can-opener” perforations. Scapular blades are heavily raked and shattered. Along with the strong preference for cercopithecoids, these distinct patterns of bone survival and damage indicate the feasibility of recognizing specific taphonomic signatures of large raptors in fossil assemblages. Berger and Clarke (1995) hypothesized that crowned hawk-eagles or similar large raptors were principally responsible for the accumulation of the late Pliocene fossil fauna from Taung, South Africa, including the type infant skull of Australopithecus africanus. The results of our study suggest that the faunal composition and type of damage to the hominid skull and other bone from Taung are consistent with the predatory activities of large raptors. More rigorous assessment of their hypothesis will require sorting the Taung fauna by locality and further detailed analysis of species composition and bone damage and survivability patterns.

A primary job for Congressional staff members is to advise their bosses—senators or representatives—on issues before the U.S. Congress. As AGU's Congressional Fellow and a Senate legislative staff member, I try to provide the best possible advice to my boss, Sen. Dianne Feinstein (D-Calif.). My struggles in this regard have taught me a lot about the thorny issues involved in the interplay of science and policy. One issue on which I was asked to advise the senator is what, if anything, to do after forests are disturbed by fires or other events. Specifically, should the burned and dead wood be logged? Some people believe it is better not to log; forests regenerate naturally and ‘salvage logging’ as it is called, is ecologically harmful. Others believe logging paves the way for faster forest and habitat restoration.

I knew my undergraduate degree in anthropology would come in handy one day. I never guessed, though, that with a Ph.D. in geology and two years of postdoctoral experience under my belt (and my anthropology days far behind), AGU would choose me for a year-long, total-immersion ethnographic extravaganza of my very own. I have been dropped into the proverbial wilds, to live among the natives to attempt to understand their culture in all its byzantine ritual, hierarchy, and ceremony.