Abstract The relationship between chromosomal and morphological variation in mammals is poorly understood. We analyzed the cranial size and shape variation in Ctenomys lami concerning to the geographic variation in their chromosome numbers. This subterranean rodent occurs in a narrow range of sand-dunes in the Coastal Plain of southern Brazil. This species presents a high karyotypic variation with diploid numbers varying from 2n = 54 to 2n = 58, involving the fission and fusion of chromosome pairs 1 and 2. Due to different chromosome rearrangement frequencies along their geographic distribution, four karyotypic blocks were proposed. This study, explored cranium shape and size variation in geographical, chromosomal polymorphism, and chromosome rearrangements contexts to test whether the four karyotypic blocks reflect morphologically distinct units. For this, we measured 89 craniums using geometric morphometrics and used uni and multivariate statistics to discriminate the predicted groups and test for an association among chromosomal and morphological variation. Our results show the size and shape of sexual dimorphism, with males larger than females, and support the existence of four karyotypic blocks for Ctenomys lami based on morphological variation. However, our results do not support a direct relationship between chromosomal and cranial morphological variation in C. lami.

Resumen El objetivo fue analizar si el consumo de diferentes plantas influenciaba el tamaño/forma de las mandíbulas de larvas de lepidópteros oligófagas y si dicho consumo ocasionaba tasas de crecimiento diferenciadas entre el músculo aductor mandibular y las mandíbulas durante su ontogénesis. Para esto se usaron larvas de Heliconius erato criadas en cuatro plantas hospederas naturales, a las que se les tomaron medidas de longitud de cápsula cefálica, tamaño mandibular y área del músculo aductor. Para detectar eventuales diferencias de forma mandibular se empleó microscopía electrónica y morfometria geométrica, y para posibles cambios alométricos se realizaron comparaciones entre curvas de crecimiento mandíbula vs. músculo aductor de los individuos criados en las cuatro plantas hospederas. Se encontró que no existen diferencias de tamaño entre las mandíbulas ni en músculos aductores de individuos criados en las diferentes plantas pero la forma mandibular fue significativamente diferente, mostrando una relación directa con la planta hospedera usada como alimento. Generalmente, la mandíbula creció proporcionalmente más que el músculo aductor, cuyo crecimiento fue estable. El cambio más significativo fue el alargamiento de los dientes incisivos en mandíbulas de larvas criadas con Passiflora suberosa. Se sugiere que esto se debe a que las hojas de esta especie poseen mayor dureza comparadas con las otras y que el desarrollar dientes largos facilitaría su corte y consumo.

Abstract This study aimed to test whether the consumption of different host plants influences the size and shape of mandibles and associated muscles in oligophagic insects throughout ontogeny. Larvae of Heliconius erato phyllis (Lepidoptera: Nymphalidae) were reared on four species of passion vines (Passifloraceae) and had the size of their head caspules, mandibles and associated adductor muscles measured afterward. Corresponding effects on shape and potential allometries in mandibles were also evaluted using geometric morphometric analysis based on scanning electron micrographs. Growth in mandibular size was greater compared to that of associated adductor muscles. There was no host plant effect on the sizes of either mandibles or adductor muscles. However, the shapes of mandibles was significantly different among passion vine species used as larval food. Greater differences in shape associated with wider teeth were obtained for Passiflora suberosa, whose leaves are tougher compared to those of P. misera, P. caerulea, and P. actinia; and, among which there was no difference in manbilular shape. Thus, it was inferred that the larval stage of this Heliconius species is able to adjust its mandible shape according to the toughness of host plants; a phenotypic plasticity mechanism that can be supposed to have evolved in order to facilitate processing these kinds of leaves.

Abstract We tested the association between chromosomal polymorphism and skull shape and size variation in two groups of the subterranean rodent Ctenomys. The hypothesis is based on the premise that chromosomal rearrangements in small populations, as it occurs in Ctenomys, produce reproductive isolation and allow the independent diversification of populations. The mendocinus group has species with low chromosomal diploid number variation (2n=46-48), while species from the torquatus group have a higher karyotype variation (2n=42-70). We analyzed the shape and size variation of skull and mandible by a geometric morphometric approach, with univariate and multivariate statistical analysis in 12 species from mendocinus and torquatus groups of the genus Ctenomys. We used 763 adult skulls in dorsal, ventral, and lateral views, and 515 mandibles in lateral view and 93 landmarks in four views. Although we expected more phenotypic variation in the torquatus than the mendocinus group, our results rejected the hypothesis of an association between chromosomal polymorphism and skull shape and size variation. Moreover, the torquatus group did not show more variation than mendocinus. Habitat heterogeneity associated to biomechanical constraints and other factors like geography, phylogeny, and demography, may affect skull morphological evolution in Ctenomys.

ABSTRACT Changes in the landscape where watersheds are located may affect the stream biota in different ways. In order to explore this idea, we collected freshwater crabs of the genus Aegla Leach, 1820 in subtropical region of southern Brazil. We also measured a number of landscape features and physico-chemical variables in the collection streams and surroundings in order to ascertain which factors affect the occurrence of these crustaceans. A total of 167 individuals of Aegla were collected in 21 streams. The collection was comprised of three species: A. odebrechtii, A. platensis, and A. singularis. The occurrence of A. platensis was influenced by physico-chemical variables (total carbon and total organic carbon) and stream morphometry factors (level curves sum). The occurrence of A. singularis was influenced by land use (pasture and exposed soil and agriculture) and the stream morphometry (level curves sum). Only a small number of A. odebrechtii were collected and their occurrence was influenced by land use (pasture and exposed soil and agriculture). The topography of the area studied limits the types of land use and areas that are less favorable for agriculture (more hilly areas) are have more riparian vegetation (or less anthropic stress). As a result, these areas are less subject to changes in water quality, which is reflected in the distribution of Aegla species.

RESUMEN Los cambios en el paisaje donde se ubican las cuencas hidrográficas pueden afectar la corriente de diferentes maneras. Con el fin de explorar esta idea, se recogieron los cangrejos de agua dulce del género Aegla Leach, 1820 en la región subtropical del sur de Brasil. También se midió una serie de características del paisaje y las variables físico-químicas en los arroyos de colección y el entorno con el fin de determinar qué factores afectan la ocurrencia de estos crustáceos. Un total de 167 individuos de Aegla fueron recolectados en 21 arroyos. La colección estaba compuesta por tres especies: A. odebrechtii, A. platensis y A. singularis. La ocurrencia de A. platensis estuvo influenciada por variables fisicoquímicas (carbono total y carbono orgánico total) y morfometría (suma de curvas de nivel). La ocurrencia de A. singularis estuvo influenciada por el uso de la tierra (pastos y suelo expuesto y agricultura) y la morfometría (suma de curvas de nivel). Sólo un pequeño número de A. odebrechtii fueron recolectados y su ocurrencia fue influenciada por el uso de la tierra (pastos y suelo expuesto y la agricultura). La topografía del área estudiada limita los tipos de uso de la tierra y las áreas menos favorables para la agricultura (zonas más montañosas) tienen más vegetación ribereña (o menos estrés antrópico). Como resultado, estas áreas están menos sujetas a cambios en la calidad del agua, lo que se refleja en la distribución de las especies de Aegla.

RESUMO A variação geográfica no tamanho e forma do crânio do rato-do-pântano Scapteromys tumidus foi examinada em amostras de oito clusters geográficos, abrangendo a maior parte da distribuição no sul do Brasil e no Uruguai, usamos dois métodos de geometria morfométrica bidimensional para as vistas dorsal, ventral e lateral do crânio. Os descritores geométricos não mostraram diferenças significativas no tamanho do crânio entre os clusters geográficos, enquanto que as diferenças na forma foram altamente significativas. Encontramos correlação significativa e moderada entre distâncias geográficas e morfológicas, corroborando o modelo de isolamento-por-distância. Amostras da planície costeira central do Rio Grande do Sul foram as mais diferenciadas, segregando completamente de todas as outras amostras na análise de variáveis canônicas para a vista dorsal. As regiões visivelmente mais variáveis no crânio foram o arco zigomático (principalmente a raiz esquamosal do zigomático) e as bordas laterais da caixa craniana. Uma vez que a correlação entre as distâncias geográfica e morfológica não foi alta, é possível que outros fatores (heterogeneidade ambiental e/ou barreiras geográficas) venham atuando na diferenciação do crânio de S. tumidus.

ABSTRACT The geographic variation in skull size and shape of the swamp rat Scapteromys tumidus was examined in samples from eight geographic clusters in almost of its distribution in southern Brazil and Uruguay. For analysis we used two-dimensional geometric morphometric methods for dorsal, ventral and lateral views of the skull. The geometric descriptors showed no significant differences in skull size between geographic clusters, while differences in shape were highly significant. We found a significant and moderate correlation between geographic and morphological distances, corroborating the isolation-by-distance model. Samples from the Rio Grande do Sul central coastal plain were the most differentiated, segregating completely from all other samples in canonical variate analysis for the dorsal view. The most visible variable regions in skull were the zygomatic arch (mainly the squamosal root of zygomatic) and the lateral braincase borders. Once correlation between geographic and morphological distances were not strong, it is possible that other factors (environmental heterogeneity and/or geographic barriers) may are acting in S. tumidus skull differentiation.

Resumo Objetivo O objetivo deste estudo foi avaliar os efeitos de usos da terra em bacias de drenagem de riachos sobre a composição taxonômica e funcional das comunidades de invertebrados aquáticos associados a detritos foliares. Métodos Avaliamos a colonização de invertebrados em detritos de plantas incubadas em riachos com presença e ausência de vegetação ripária e diferentes usos da terra na área de drenagem. Utilizamos a abordagem de litter bags. Resultados A composição taxonômica e funcional da fauna de invertebrados associados aos detritos variou entre os riachos. Além disso, os riachos com presença de vegetação mostraram comunidades com menor variação taxonômica e funcional. Ainda, a densidade de invertebrados fragmentadores foi menor nos riachos sem vegetação. Conclusões A porcentagem de vegetação ripária é um fator ambiental importante na composição dos invertebrados. Porém, os usos da terra em toda a bacia de drenagem devem ser considerados como fatores relevantes na estruturação da biota aquática.

Abstract Aim Our aim in this study was to evaluate the effects of land use in drainage basins of the streams on the taxonomic and functional composition of aquatic invertebrate communities associated in leaf litter. Methods We evaluated the colonisation of invertebrates in the incubated plant debris in streams with presence and absence of riparian vegetation and different land-uses in the drainage area. We used the litter bags approach. Results The taxonomic and functional composition invertebrate associated with leaf litter ranged between streams. In addition, streams with presence of vegetation showed less variation taxonomic and functional composition communities. Still, the density of shredders invertebrates were lower in streams without vegetation. Conclusions The riparian vegetation is an important environmental factor in the composition of invertebrates. However, the land-use throughout the drainage basin should be considered as relevant factor in structuring aquatic biota.