Functional morphology and paleobiology of the pliocene rodent Actenomys (Caviomorpha: Octodontidae): the evolution to a subterranean mode of life

The Pliocene caviomorph rodent Actenomys has long been recognized as an early fossorial representative of the subfamily Ctenomyinae (Octodontidae), which includes one living genus, Ctenomys (tuco-tucos), and several species widely distributed in South America. To assess the de gree of specialization for digging in Actenomys , we performed morphological comparisons with other octodontid genera (Octodon, Spalacopus , and Ctenomys) of known mode of life and behaviour. As a whole, our results indicate that, in terms of morphological specializations for digging, Actenomys occupies an intermediate position between Octodon , a generalized semi-fossorial rodent which forages above ground, and Ctenomys-Spalacopus , two highly specialized subterranean forms. The position of the deltoid process (humerus) and the length of the olecranon process (ulna)–two traits which affect the out-forces exerted by several forelimb muscles–were in Actenomys intermediate between non-subterranean and subterranean taxa. The skull, particularly the rostrum, appears to be strong, and sagittal and nuchal crests are well marked. The zygomatic arches arc as flared as those of the generalized Octodon. Notably, the upper and lower incisors of Actenomys were extremely procumbent, as in many highly-specialized chisel-tooth digging species. Based upon the stratigraphic and sedimentological analysis of the palaeosoils containing its fossil remains, we suggest that Actenomys lived in an environment of moderate to hig primary productivity. The texture of the palaeosoils indicate that theywere hard and highly cohesive. This situation, which contrasts with that observed in living Ctenomyinae, has relevant implications for burrowing cost. The integration of morphological and palaeoenvironmental data allowed testing of hypotheses about the palaeobiological attributes of this ancestral ctenomyine.     

Fertility table and rate of population growth of the predator Supputius cincticeps (Heteroptera: Pentatomidae) on one plant of Eucalyptus cloeziana in the field

The reproductive potential and population growth (r_m and λ) of the predator Supputius cincticeps (Heteroptera: Pentatomidae) were evaluated using a life and fertility table. S. cincticeps was reared on one plant of Eucalyptus cloeziana in the field and fed with Tenebrio molitor (Coleoptera: Tenebrionidae) pupae. Females of this predator had a net reproductive rate (R₀) of 21.02 females/female; an intrinsic rate of population increase (r_m) of 0.041 and finite rate of increase (λ) of 1.042. This resulted in population growth of S. cincticeps in the eucalyptus plant with a doubling time of 17.01 days. This natural enemy can be reared under field conditions with alternative prey for use in biological control. Such individuals of S. cinticeps will be better adapted to field conditions when they are liberated.     

Contribution of transpiration to forest ambient vapour based on isotopic measurements

Using a simple isotope mixing model, we evaluated the relative proportion of water vapour generated by plant transpiration and by soil evaporation at two sites in the Amazon basin. Sampling was carried out at two different soil covers (forest and pasture), in a seasonal tropical rainforest at eastern Amazon where major deforestation is the result of land-use change, and compared to a less seasonal central Amazon forest. In both forests, vapour from transpiration was responsible for most, if not all, of the water vapour generated in the forest, while it could not be detected above the grassy pastures. Thus the canopy transpiration may be a major source of water vapour to the forest and perhaps to the atmosphere during the dry season. The results are discussed in relation to predictive models based on net radiation that usually are not able to distinguish between transpiration and evaporation.     

A general survey and some taxonomic implications of diterpenes in the Asteraceae

This paper provides a general survey of the occurrence of diterpenes in the Asteraceae. Data on 4351 botanical occurrences were obtained from the literature. These were grouped by skeleton for each genus. Then, the genera were grouped by subtribes, which, in turn, were gathered in tribes, followed by subfamilies. In spite of the low number of species containing diterpenes, it was possible to describe some structural features of these compounds, i.e. the skeletal types in various taxa and the positions in some skeletons that are always oxidized or never undergo oxidation in some genera. Thus, it was verified that: in the subfamily Cichorioideae, only a few of the studied species possess diterpenes, wherein kaurane is the most frequent diterpene skeleton. In the Asteroideae, the presence of diterpenes is much greater than that in the Cichorioideae and Carduoideae. At tribal taxonomic level, for example, the Astereae produce labdanes and clerodanes; Heliantheae and Eupatorieae produce kauranes and labdanes, respectively; and Calenduleae produce pimaranes. Some taxonomic implications are presented.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 291–308.     

Sex‐specific evolution of bite performance in Liolaemus lizards (Iguania: Liolaemidae): the battle of the sexes

Although differential selective pressures on males and females of the same species may result in sex‐specific evolutionary trajectories, comparative studies of adaptive radiations have largely neglected within‐species variation. In this study, we explore the potential effects of natural selection, sexual selection, or a combination of both, on bite performance in males and females of 19 species of Liolaemus lizards. More specifically, we study the evolution of bite performance, and compare evolutionary relationships between the variation in head morphology, bite performance, ecological variation and sexual dimorphism between males and females. Our results suggest that in male Liolaemus, the variation in bite force is at least partly explained by the variation in the degree of sexual dimorphism in head width (i.e. our estimate of the intensity of sexual selection), and neither bite force nor the morphological variables were correlated with diet (i.e. our proxy for natural selection). On the contrary, in females, the variation in bite force and head size can, to a certain extent, be explained by variation in diet. These results suggest that whereas in males, sexual selection seems to be operating on bite performance, in the case of females, natural selection seems to be the most likely and most important selective pressure driving the variation in head size. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 461–475.     

Using gap‐crossing capacity to evaluate functional connectivity of two Atlantic rainforest birds and their response to fragmentation

Abstract One of the main consequences of habitat loss and fragmentation is the increase in patch isolation and the consequent decrease in landscape connectivity. In this context, species persistence depends on their responses to this new landscape configuration, particularly on their capacity to move through the interhabitat matrix. Here, we aimed first to determine gap‐crossing probabilities related to different gap widths for two forest birds (Thamnophilus caerulescens, Thamnophilidae; and Basileuterus culicivorus, Parulidae) from the Brazilian Atlantic rainforest. These values were defined with a playback technique and then used in analyses based on graph theory to determine functional connections among forest patches. Both species were capable of crossing forest gaps between patches, and these movements were related to gap width. The probability of crossing 40 m gaps was 50% for both species. This probability falls to 10% when the gaps are 60 m (for B. culicivorus) or 80 m (for T. caerulescens). Actually, birds responded to stimulation about two times more distant inside forest trials (control) than in gap‐crossing trials. Models that included gap‐crossing capacity improved the explanatory power of species abundance variation in comparison to strictly structural models based merely on patch area and distance measurements. These results highlighted that even very simple functional connectivity measurements related to gap‐crossing capacity can improve the understanding of the effect of habitat fragmentation on bird occurrence and abundance.     

The effects of shrimps on benthic material in a Brazilian island stream

1. Shrimps are abundant in many tropical coastal streams. Studies in Central America and the Caribbean have demonstrated the importance of shrimps in removing sediments and altering the composition of the benthos. Previous work in our study area showed that ephemeropterans and not shrimps were important in removing benthic material. 2. Here we used an experimental exclusion to test the hypothesis that shrimps exert strong influence on sediment dynamics with direct and indirect effects on the benthic algal and faunal community at a site where they are the predominant element of macrofauna. We used electricity to exclude Macrobrachium olfersi and Potimirim glabra from small quadrats (0.135 m²) for 34 days in a stream located at Ilha Grande, Rio de Janeiro state, Brazil. We analysed benthic sediment dynamics and community colonisation during this period on artificial substrates in electrified and not‐electrified quadrats. 3. Significantly higher sediment accrual had occurred in the electrified treatment after 14 days and persisted for the 34‐day course of the experiment; substrates protected from shrimps contained about four times as much ash‐free dry mass (AFDM) as those of the controls. After 34 days, significantly more pennate diatoms were present in the exclusion treatment, but chlorophyll was not significantly different between treatments. Densities of baetid ephemeropteran nymphs were significantly higher in the presence of shrimps. 4. We attribute all these effects to the atyid P. glabra, the more abundant and active shrimp observed in the control treatment. Our results suggest that atyid shrimps played an important role related to sediment removal on hard substrate by direct ingestion and ‘bioturbation’. They reduced certain components of the periphyton (pennate diatoms) without affecting primary production (chlorophyll a). The activity of these shrimps on periphyton affected also faunal components such as baetid ephemeropterans and seems to determine the composition of the benthic community.     

Karyotype differentiation among Spondias species and the putative hybrid Umbu-cajá (Anacardiaceae)

Spondias L. comprises at least nine Neotropical species, including the widely cultivated S. monbim and S. tuberosa. Umbu‐cajá, a putative hybrid between these two species, is also grown. In this paper, the karyotypes of five Spondias species and Umbu‐cajá were analysed for evidence of this hybridization. Chromosome banding with chromomycin A₃ and the distribution of 5S and 45S rDNA sites were used to characterize the plants, also genomic in situ hybridization using nuclear DNA from both putative parents and the hybrid as probes. All material presented the same chromosome number (2n = 32) and morphology, but differed in the number and distribution of bands. Spondias monbim and S. tuberosa, the supposed relatives of Umbu‐cajá, displayed similar banding patterns, with five to six chromosome pairs having terminal bands, whereas Umbu‐cajá exhibited bands on both members of nine chromosome pairs. The three other species, S. venulosa, S. cytherea and S. purpurea, showed less closely related karyotypes, with bands in 12–18 chromosome pairs. In situ hybridization with 5S and 45S rDNA probes revealed one site of each probe per haploid chromosome complement in all material. However, in S. tuberosa, the location of 5S rDNA was different from the other species and found no counterpart in Umbu‐cajá. Several tests with total DNA from S. mombin and S. tuberosa against metaphase chromosomes of Umbu‐cajá failed to differentiate the individual genomes in the hybrid. From the chromosome banding and the distribution of rDNA sites, as well as from the genomic in situ hybridization, it seems clear that Umbu‐cajá is related closely to S. monbim and S. tuberosa, but it is karyotypically homozygous and distinct from theses other species. Karyotypically, the three other investigated species were related less closely to Umbu‐cajá. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 541–547.     

New studies on allozyme genetic distance and variability in akodontine rodents (Cricetidae) and their systematic implications

Allozyme genetic distance and variability were studied by horizontal starch gel electrophoresis in 11 species of rodents of the tribe Akodontini representing four different genera. One species of the phyllotine Calomys was used as an outgroup for comparisons. Thirty presumptive loci were assessed in a total of 172 specimens. Only three of 30 loci were found to be monomorphic in the whole sample. Levels of polymorphism ( P ) and mean heterozygosity ( H ) were dependent on esterase loci which increase H values by 6.26% on average. Nei's jackknife genetic distances among conspecific populations were found not to differ significantly with geographic distance. Phenetic and cladistic interspecific analysis coincided in indicating the monophyletic nature of the akodontine clade, and its splitting into two sharply differentiated subclades: one comprising species referred to as Abrothrix, Chelemys and Geoxus , another comprising species of Akodon (including Deltamys ) and Oxymycterus. Thus, the separateness of a southern Andean branch in the cladogenesis of the Akodontini was confirmed, as well as the early recognition of Abrothrix as a full genus, and the recent claim of Spotorno to include in this genus other species formerly classified as Akodon jelskii, Ak. andinus and Ak. olivaceus.