Cetartiodactyla: Updating a time-calibrated molecular phylogeny.

Cetartiodactyla comprises one of the most diverse mammal radiations. Currently, 23 families, 131 genera and more than 330 species are recognized. Several studies have been trying to resolve its phylogenetic relationships. The most comprehensive dated phylogenetic hypothesis available includes only 55% of the extant species, precluding a clear understanding of ecological and evolutionary patterns in Cetartiodactyla. Here, we gathered all mitochondrial genetic data available in GenBank to build a robust Cetartiodactyla calibrated phylogenetic tree using 21 fossil calibration points. We found mitogenomic data for 225 species and included other 93 species from which there was at least one mitochondrial gene available. Using a Bayesian approach, we generated a dated tree comprising 90% of the extant Cetartiodactyla species (n = 318). The major lineages showed robust support and families divergence times are congruent with the available fossil evidence and with previously published phylogenetic hypotheses. By making available a dated phylogeny with extensively sampled clades, we expect to foster future studies on the origin, tempo and mode of Cetartiodactyla diversification.

Ontogenetic allometry conservatism across five teleost orders.

Geometric morphometrics were used to analyse ontogenetic trajectories in representatives of the Characiformes, Cichliformes, Cyprinodontiformes, Siluriformes, and Tetraodontiformes. It was not possible to differentiate any allometric growth patterns across groups, indicating that a phylogenetically conserved developmental pattern is widespread throughout Teleostei.

Neo-sex Chromosomes in the Maculipennis Species Group (Dichroplus: Acrididae, Melanoplinae): The Cases of D. maculipennis and D. vittigerum.

South American melanopline grasshoppers display a disproportionate number of derived karyotypes, including many cases of neo-sex chromosome systems. This is especially true of the genus Dichroplus and its Maculipennis species group. We analyzed the karyotype and neo-sex chromosomes in mitosis and meiosis of Dichroplus maculipennis and D. vittigerum from Argentina using conventional and fluorescent cytogenetic protocols in order to elucidate the behavior and origin of these neo-XY systems in relation to the current phylogeny of this group. Our results showed that D. maculipennis (2n = 22♂/22♀; neoXY/neoXX) and D. vittigerum, whose karyotype is described here for the first time (2n = 18♂/18♀; neoXY/neoXX), show highly evolved neo-XY systems, although with significant differences between them. Furthermore, both species differ for two autosomal fixed Robertsonian fusions present in D. vittigerum. Analysis of karyotypic character state optimization strongly suggests the independent origin and evolution of neo-sex systems within this species group.

Preferential accumulation of sex and Bs chromosomes in biarmed karyotypes by meiotic drive and rates of chromosomal changes in fishes.

Mechanisms of accumulation based on typical centromeric drive or of chromosomes carrying pericentric inversions are adjusted to the general karyotype differentiation in the principal Actinopterygii orders. Here, we show that meiotic drive in fish is also supported by preferential establishment of sex chromosome systems and B chromosomes in orders with predominantly bi-brachial chromosomes. The mosaic of trends acting at an infra-familiar level in fish could be explained as the interaction of the directional process of meiotic drive as background, modulated on a smaller scale by adaptive factors or specific karyotypic properties of each group, as proposed for the orthoselection model.

Bergmann's rule across the equator: a case study in Cerdocyon thous (Canidae).

1. The variation in cranial size of the crab-eating fox Cerdocyon thous was analysed in relation to latitude and several environmental variables throughout its distribution in South America. 2. We tested the existence of clines to determine whether this canid follows Bergmann's rule to the north and south of the Equator. Also, using niche modelling, we analysed whether the climatic changes during the last glaciation could have influenced Bergmann's rule in this species. We quantified the size of the cranium of C. thous (n = 300). The data were divided into two groups: (i) south of the Equator (n = 163) and (ii) north of the Equator (n = 137). We performed correlations, OLS regressions and simultaneous autoregressions to analyse the relationship between the variation in size and different geographic and environmental variables. Data of occurrence (n = 594) together with ambient variables from the present and the last glacial maximum (LGM) were used to predict the occurrence of C. thous with the implementation of the maximum entropy method. Present-day and historical distribution maps were obtained. 3. The variation in the size of the cranium of C. thous showed two trends. In the south of Equator, we observed that the size of the skull shows an inverse relationship with temperature-related variables and a positive one with precipitation, while in north of the Equator, we observed the opposite relationship. Populations south of the Equator follow Bergmann's rule showing increasing size with increasing latitude. To the north of the Equator, a non-Bergmannian pattern occurs because size decreases with increasing latitude. 4. Niche modelling showed two present-day groupings in South America, one north of Amazonia and the other south. However, for the period of the LGM, four groups emerged, possibly related to the four subspecies presently described for C. thous. Therefore, it is possible that the observed pattern - southern populations following Bergmann's rule while northern populations reflecting the opposite - has been influenced by the events that occurred during the LGM that could have led to the differentiation of populations.

Morphological, genetic, and chromosomal variation at a small spatial scale within a mosaic hybrid zone of the grasshopper Dichroplus pratensis Bruner (Acrididae).

Hybrid zones are regions where genetically different populations meet and mate, resulting in offspring of mixed characteristics. In organisms with limited dispersal, such as melanopline grasshoppers, hybrid zones can occur at small spatial scales (i.e., <500 m). We assessed levels of morphological, chromosomal, and molecular variability in adult males of the grasshopper Dichroplus pratensis Bruner (N = 137 males, 188 females) collected at 12 sites within a mosaic hybrid zone in a heterogeneous environment in Sierra de la Ventana, Argentina. In this hybrid zone, 2 Robertsonian chromosomal races, polymorphic for different centric fusions, meet (the "Northern race" at low altitudes and the "Southern race" at higher altitudes), forming hybrids that show monobrachial homologies during meiosis. High morphometric variation in 6 traits was revealed among grasshoppers of both sexes, with male body size positively and significantly correlated with increasing altitude. Frequency of Robertsonian fusions characteristic of the Southern race increased significantly with altitude. Moreover, fusion frequencies covaried between samples. Considerable genetic variation was revealed by random amplification of polymorphic DNA markers, with heterozygosity ranging from 0.3477 to 0.3745. Insects from low-altitude and high-altitude populations showed significant genetic differentiation, as indicated by F(ST) values. The proposed model for D. pratensis, involving the generation and maintenance by chromosomal fusions, of gene complexes adaptive in different environments, could explain the observed clinal patterns within the contact zone.

Neo-sex chromosome diversity in Neotropical melanopline grasshoppers (Melanoplinae, Acrididae).

We report the results of a study on the neo-sex chromosome systems of six Neotropical Melanoplinae species for contributing to a better understanding of their origin and behaviour of these systems. Our analyses included detailed descriptions of the structure and behaviour of the sex chromosome configurations in male and female meiosis of species belonging to the genera Ronderosia, Dichromatos and Atrachelacris. Three species, R. forcipatus, R. malloi and A. unicolor, showed typical Robertsonian fusion-derived neo sex-chromosomes. However, the male metaphase I orientation of R. bergi sex pair indicated that more than one rearrangement was involved in its origin. The two species of Dichromatos presented a multiple neo-X(1)X(2)Y/X(1)X(1)X(2)X(2) sex system, with two Robertsonian fusions involved in their genesis. Observations of female meiosis, confirmed the nature of the sex-chromosomes analyzed. Our results also showed different degrees of homology divergence between the neo-sex chromosomes and emphasize the plasticity of the chromosome complement of the Neotropical Melanoplinae to establish Robertsonian fusions and generate novel sex-chromosome systems. We also discuss karyotypic diversity within this group in terms of the centromeric drive theory of chromosomal evolution.

A test of Allen's rule in ectotherms: the case of two south American Melanopline Grasshoppers (Orthoptera: Acrididae) with partially overlapping geographic ranges.

We studied the geographic variation of three morphometric characters in relation to body size in two South American grasshoppers (Acrididae), Dichroplus vittatus Bruner and D. pratensis Bruner to test Allen's rule in these ectotherms. Since both species follow the converse to Bergmann's rule owing to latitudinal and/or altitudinal variation in time available for growth and reproduction, geographic variation in body size proportions of protruding parts may obey to differential allometric growth in different geographic areas. Alternatively, it could reflect true Allenian variation related to thermoregulation. Body proportions were studied by correlation/regression analyses with geographic and climatic variables. In D. pratensis, body proportions increased with latitude and decreased with altitude. These results probably obey to the effects of water balance and seasonality on final body size, and on the allometric growth of the three studied characters not being related to thermoregulation. In D. vittatus, a generally non-significant trend towards the decrease of the mean proportions of all three characters with increasing latitude was observed. Nevertheless, also in this species, it is probable that the environmental gradient responds to seasonality factors (although not to water balance) that affect the length of growing season and, in consequence, body size and its allometric relationships. We conclude that the regularities in the geographic distribution of body proportions of D. pratensis and D. vittatus do not follow Allen's rule in the sense of thermoregulation, and result from variables that determine growing season length and the allometric growth of different body parts.

A test of Allen's rule in ectotherms: the case of two south American Melanopline Grasshoppers (Orthoptera: Acrididae) with partially overlapping geographic ranges / Un test de la regla de Allen en ectotermos: el caso de dos Saltamontes Melanoplinos (Orthoptera: Acrididae) sudamericanos con distribuciones Geográficas parcialmente solapadas

We studied the geographic variation of three morphometric characters in relation to body size in two South American grasshoppers (Acrididae), Dichroplus vittatus Bruner and D. pratensis Bruner to test Allen's rule in these ectotherms. Since both species follow the converse to Bergmann's rule owing to latitudinal and/or altitudinal variation in time available for growth and reproduction, geographic variation in body size proportions of protruding parts may obey to differential allometric growth in different geographic areas. Alternatively, it could reflect true Allenian variation related to thermoregulation. Body proportions were studied by correlation/regression analyses with geographic and climatic variables. In D. pratensis, body proportions increased with latitude and decreased with altitude. These results probably obey to the effects of water balance and seasonality on final body size, and on the allometric growth of the three studied characters not being related to thermoregulation. In D. vittatus, a generally non-significant trend towards the decrease of the mean proportions of all three characters with increasing latitude was observed. Nevertheless, also in this species, it is probable that the environmental gradient responds to seasonality factors (although not to water balance) that affect the length of growing season and, in consequence, body size and its allometric relationships. We conclude that the regularities in the geographic distribution of body proportions of D. pratensis and D. vittatus do not follow Allen's rule in the sense of thermoregulation, and result from variables that determine growing season length and the allometric growth of different body parts.

Estudiamos la variación geográfica de tres caracteres morfométricos en relación al tamaño corporal, en dos saltamontes sudamericanos (Acrididae), Dichroplus vittatus Bruner y D. pratensis Bruner, para verificar la regla de Allen en ectotermos. Ambas especies siguen la regla de Bergmann inversa por variación latitudinal y/o altitudinal en el tiempo disponible para crecimiento y reproducción; entonces la variación de proporciones de partes salientes del cuerpo, obedecería a crecimiento alométrico diferencial en diferentes áreas geográficas. Alternativamente, podría reflejar variación alleniana relacionada a termorregulación. Las proporciones corporales se estudiaron por análisis de correlación/regresión con variables geográficas y climáticas. En D. pratensis, las proporciones corporales aumentaron con la latitud, y decrecieron con la altitud. Esto probablemente obedezca a efectos del balance hídrico y la estacionalidad sobre el tamaño corporal final, y al crecimiento alométrico de los tres caracteres independientemente de la termorregulación. En D. vittatus, se observó una tendencia generalmente no significativa al decrecimiento de las proporciones de los tres caracteres con el incremento de latitud. Sin embargo, también es probable que el gradiente ambiental responda a factores de estacionalidad que afectan la duración de la estación de crecimiento y, consecuentemente, el tamaño corporal y sus relaciones alométricas. Concluimos qué las relaciones alométricas en la distribución geográfica de proporciones corporales de D. pratensis y D. vittatus no siguen la regla de Allen en el sentido de la termorregulación, y son el resultado de variables que determinan la duración de la estación de crecimiento y el crecimiento alométrico de diferentes partes del cuerpo.

Micro-and macrospermatid production induce by meiotically unstable B-chromosomes in two species of grasshoppers (Acrididae)

Os efeitos dos cromossomos B na formaçäo de esperma anormal (no haplóide) foram investigados em duas espécies de gafanhotos, Dichroplus pseudopunctulatus e Sinipta dalmani. Um pequeno cromossomo B telocéntrico foi estudado em machos da primeira espécie. Quando o B se encontrava em dose simples, ele apresentava um comportamento muito irregular que incluia retardo nas primeira e segunda divisöes meióticas. Como resultado, foram observados grandes números de microespermátides portadoras do B atrasado nos machos B. Um macho que possui dois cromossomos B näo mostrou um aumento significativo na produçäo de microespermátides, fato este que está correlacionado com o comportamento meiótico regular do bivalente B. Näo foi observado aumento na produçäo de macroespermátides nos machos portadores do B, e é evidente que um mecanismo de eliminaçäo age sobre o cromossomo B desta espécie. Em S.dalmani foram encontrados dois pequenos cromossomos B; um deles induzia divisäo celular defeituosa, provavelmente através do seu comportamento meiótico falho, resultando em grande proporçäo de espermátides diplóides (cerca de 50%), com consequente reduçäo de fertilidade. Os efeitos dos cromossomos B na freqüência de quiasmas foram também registrados. Os efeito do B de D.pseudopunctulatus aumentava significativamente a freqüência média de quiasmas por célula, enquanto que, inesperadamente, os cromossomos B de S.dalmani pareciam diminuir a freqüência de quiasmas significativamente. A conseqüência da produçäo incrementada de esperma anormal e a modificaçäo das freqüências de quiasmas através da presença de cromossomos B säo avaliadas em termos de seus resultados evolutivos e citológicos