Mammal disparity decreases during the Cretaceous angiosperm radiation

Fossil discoveries over the past 30 years have radically transformed traditional views of Mesozoic mammal evolution. In addition, recent research provides a more detailed account of the Cretaceous diversification of flowering plants. Here, we examine patterns of morphological disparity and functional morphology associated with diet in early mammals. Two analyses were performed: (i) an examination of diversity based on functional dental type rather than higher-level taxonomy, and (ii) a morphometric analysis of jaws, which made use of modern analogues, to assess changes in mammalian morphological and dietary disparity. Results demonstrate a decline in diversity of molar types during the mid-Cretaceous as abundances of triconodonts, symmetrodonts, docodonts and eupantotherians diminished. Multituberculates experience a turnover in functional molar types during the mid-Cretaceous and a shift towards plant-dominated diets during the late Late Cretaceous. Although therians undergo a taxonomic expansion coinciding with the angiosperm radiation, they display small body sizes and a low level of morphological disparity, suggesting an evolutionary shift favouring small insectivores. It is concluded that during the mid-Cretaceous, the period of rapid angiosperm radiation, mammals experienced both a decrease in morphological disparity and a functional shift in dietary morphology that were probably related to changing ecosystems.     

Mandibular allometry and male dimorphism in a group of obligately mycophagous beetles (Insecta: Coleoptera: Staphylinidae: Oxyporinae)

Analyses of seven species of the obligately mycophagous staphylinid beetle genus Oxyporus indicate that five species display male mandibular allometry. Among species with dimorphic separations, two general allometric patterns were observed: (1) change in mandibular length at a hypothesized switch point is discontinuous rather than continuous, and (2) the linear slope of mandibular length versus elytral length changes at the hypothesized switch point. The male dimorphisms are likely related to male mating strategies where minor males increase the chances to encounter females by maintaining maneuverability, while major males do the same through intraspecific combat. Male dimorphisms may also be correlated with patterns of fungal usage.     

A new form of insect cuticle

A hitherto unnoticed, harder form of cuticle, which occurs on the mandibles of the Australian plague locust, Chortoicetes terminifera , is described     

Cuticular microstructure of Australian ant mandibles confirms common appendage construction

Exoskeletons characterise Arthropoda and have allowed the morphological and taxonomic diversity of the phylum. Exoskeletal sclerotisation occurs in genetically designated regions, and mandibles represent one such area of high sclerotisation. Mandible morphology reflects dietary preferences and niche partitioning and has therefore been well documented. However, mandibular cuticular microstructure has been under-documented. Here we use scanning electron microscopy to explore mandible microstructure in four disparate Australian Formicidae taxa (ants) with different life modes and diets: Camponotus nigriceps, Iridomyrmex purpureus, Odontomachus simillimus and Rhytidoponera aciculata. We test the hypothesis that mandible construction is highly conserved across these species, as would be expected for arthropod cuticle. We show broadly similar mandible microstructure but report that pore canals and cuticular indentations are not ubiquitous among all studied taxa. Our preliminary results demonstrate that ant taxa have morphologically plastic mandibles with a highly conserved construction, potentially reflecting an interesting record of evolutionary stasis.     

Soil application of silicon reduces yellow stem borer,Scirpophaga incertulas (Walker) damage in rice

The effect of soil application of rice husk ash (RHA), a cheap renewable source of silicon, and imidazole (a silicon solubilizer and carrier) on yellow stem borer (YSB), Scirpophaga incertulas (Walker), and its damage to rice plants were investigated. Treatments included soil application of RHA (T1), imidazole (T2), RHA + imidazole (applied once at vegetative stage, T3) and RHA + imidazole (applied twice at both vegetative and booting stages of crop growth, T4) with an untreated control (T5). The effect was tested in five varieties, viz., BPT 5204, KRH2, Pusa Basmati 1, MTU1010 and Vandana. All the soil treatments reduced damage by YSB at vegetative and reproductive phases across five varieties as compared to untreated control. Scanning electron micrograph and electron‐dispersive X‐ray spectrum analysis of stem tissue of rice variety BPT 5204 treated with silicon revealed the enhanced deposition of silicon in cell walls and 2.1‐ to 5.3‐fold increase in silicon content across treatments. Larvae collected from the silicon‐treated plants had worn mandibles, and the histological studies showed rupture of the peritrophic membrane, increased vacuolation, disintegration of columnar cells and discharge of cellular contents into the gut lumen due to abrasion of midgut epithelium, as compared to untreated control where the columnar cells and midgut lining were intact. Although all the treatments were effective, T4‐imidazole applied twice along with RHA was more effective in reducing YSB damage followed by T3‐imidazole applied once with RHA at tillering stage, T2‐imidazole alone and T1‐RHA in the descending order of efficacy.     

A morphometric analysis of mandibular teeth in Folsomia (Collembola: Isotomidae)

Morphological variation in the apical mandibular teeth of seven Folsomia species (F. bisetosa, F. brevicauda, F. Candida, F. fimentaria, F. inoculata, F. penicula , and F. quadrioculata) was examined by canonical variates analysis of a systematic 'truss' of measurements. Differences were found between all but two species (F. brevicauda and F. quadrioculata) showing that the morphology of 'biting-type' mouthparts can be used for species recognition. The results also show that the truss system of measurement is sensitive to small-scale differences in the mandible morphology of these insects. It is suggested that variation in mouthpart morphology, and in patterns of tooth wear, reflect differences in the feeding behaviour of Folsomia species.     

Jaw morphology and ontogeny in five species of Ophryotrocha

Detailed scanning electron microscopy of jaws within the genus Ophryotrocha (Dorvilleidae, Annelida) was performed on 871 jaw parts. The investigations resulted in new understandings of the ontogeny and jaw morphology and have systematic implications for the family. Five species in the genus (Ophryotrocha alborana, O. diadema, O. gracilis, O. hartmanni, and O. labronica pacifica) were kept in culture, and the development of the jaws was studied by sampling throughout their life history. Ophryotrocha species have mandibular plates that remain the same throughout ontogeny, whereas the posterior shafts elongate. Both mandibular plate morphology and shaft ontogeny have species‐specific distinctions. In Ophryotrocha, the maxillae can be assigned to three to four distinct types, which are replaced by moulting. The maxillary morphology and developmental stages at which moults occur are species specific, although with broad intervals. A redefinition is given for some of the basic jaw elements, and new homologies are proposed for structures that are also present across other dorvilleid taxa. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.     

The extant Chaoborus assemblage can be assessed using subfossil mandibles

1. Assemblages of Chaoborus were examined in 80 thermally stratified southern central Canadian Shield lakes to explore whether subfossil mandibles could be useful in assemblage‐level studies of Chaoborus. 2. Chaoborus (Sayomyia) (probably Chaoborus punctipennis in this study region) and Chaoborus flavicans were the most common taxa recorded, while Chaoborus trivittatus was rarer. Chaoborus americanus was not recorded in subfossil assemblages, because no fishless lakes were included in this study. Chaoborus flavicans had higher relative abundances (%) in lakes with higher dissolved organic carbon (DOC), probably because of reduced fish predation in less transparent water. 3. Results from logistic regression indicate that patterns of presence/absence for Chaoborus mandibles in the study lakes were influenced primarily by hypolimnetic oxygen concentration, probably because of the presence or extent of a hypolimnetic refugium from fish predation. 4. Chaoborus species richness in lakes, derived from subfossil assemblages, did not differ significantly from species richness estimates derived from plankton sampling with a net. Patterns of dominance and coexistence [e.g. the widespread co‐occurrence of C. flavicans and C. (Sayomyia)] determined from subfossil assemblages agreed with previous studies of the contemporary living assemblage. 5. These results suggest that subfossil assemblages may be used as an alternative to nocturnal plankton sampling to carry out research on the community ecology of Chaoborus. 6. We propose a hierarchical conceptual model of assemblage‐level patterns of Chaoborus in temperate lakes. Chaoborus americanus dominates in fishless lakes, whereas in lakes with fish Chaoborus is typically absent where there is no anoxic hyplimnion. In lakes with anoxic strata, C. trivittatus tends to dominate in lakes with few fish; in the remaining lakes, C. flavicans and C. (Sayomyia) dominate, although C. flavicans is more relatively abundant in lakes with lower water clarity (higher DOC).     

Morph‐dependent form of asymmetry in mandibles of the stag beetle Prosopocoilus inclinatus (Coleoptera: Lucanidae)

Abstract 1. The form of asymmetry in bilateral organs usually follows the same pattern within single populations. However, some exceptions may occur when a population consists of different phenotypes that are from different ontogenic backgrounds and under different selective pressures. We investigated the asymmetric patterns of mandibles of larvae, females, and males in the stag beetle Prosopocoilus inclinatus. 2. Larval mandibles exhibited directional asymmetry both in length and cross direction, whereas female mandibles showed directional asymmetry in cross direction. These asymmetric structures might be more effective in cutting wood fibres. 3. For the relation of male mandible length to body size, a model with a switch point showed a better fit to the data than a convex curve model. This shows that the males are dimorphic with two distinct morphs. 4. The form of asymmetry in male mandible length differed between the morphs. The smaller males exhibited left‐biased directional asymmetry in common with larvae, whereas the larger males exhibited fluctuating asymmetry. 5. This is a novel finding of a morph‐dependent asymmetry. The morph‐dependent asymmetry in males may be as a result of different selection on each morph or a developmental constraint from larval mandibles to adult ones.