The homology concept and its recognition criteria are introduced and discussed, with the importance of transformational (primary) homology assessment in phylogenetic analysis emphasized. We use an ontogenetic approach to explore the setal transformational homology in polychaetotic entomobryid genera (Collembola), where tergal chaetotaxy is usually the most informative character for taxonomy. The postembryonic development of setae on terga of three species in the Sinella-Coecobrya group, Sinella curviseta, Coecobrya tenebricosa and C. aokii are studied following Szeptycki’s principle. Different chaetotaxic patterns of each tergite are homologized and classified for more than 50 species of the two genera. The taxonomical significance of chaetotaxy of abdomen V, which has been rarely studied, is evaluated and affirmed here. The system presented here is a revised and updated from Szeptycki’s system.
Although food has been proposed as a possible factor on population regulation of small mammals, evidence of food restriction in field conditions is still lacking. Food restriction is generally thought to occur in high-density years of oscillating populations of small mammals. By using two body condition indices (muscle protein concentration and cleaned carcass index), we investigated variations of body condition of the greater long-tailed hamster (Tscherskia triton) and the striped hamster (Cricetulus barabensis) in the Raoyang County of the North China Plain during a population decline- and low-phase from 1998 to 2003. Our laboratory experiments showed that food restriction reduced muscle protein concentration and cleaned carcass index of greater long-tailed hamster. We found there were significant differences in body condition of hamsters over the six years. Both the muscle protein concentration and cleaned carcass index of T. triton were significantly and positively correlated with its yearly trap successes, which reflected yearly population densities. Muscle protein concentration of C. barabensis was positively correlated with the total yield of the wheat. This observation supported the hypothesis on the in-phase relation between food resources or availability and rodent abundances. During the four seasons, muscle protein concentration of two species was highest in autumn, and lowest in summer. These two body condition indices of wild T. triton in summer and in low phases were similar to 60% food restricted animals raised in the laboratory, but significantly lower than nonfood- restricted animals. Our results indicated that malnutrition occurred in summer when food was not abundant, and in low density years with low grain production (an index reflecting food abundance of rodents) in our study region. Therefore, we concluded that food limitation may play an important role in seasonal and inter-annual population fluctuation of these two hamster species.
The intergeneric phylogeny of Lagomorpha had been controversial for a long time before a robust phylogeny was reconstructed based on seven nuclear and mitochondrial DNA sequences. However, skull morphology of several endemic genera remained poorly understood. The morphology of supraorbital processes in Lagomorpha is normally used as a diagnostic characteristic in taxonomy, but whether shape change of this structure parallels its genetic divergence has not been investigated. In this study, we conducted a comparative analysis of the skull morphology of all 12 extant genera using geometric morphometrics. These results indicated that no significant phylogenetic signal is observed in the shape change of the dorsal and ventral views of the cranium as well as in the lateral view of the mandible. The supraorbital processes also show insignificant phylogenetic signal in shape change. Similarly, mapping the centroid size (averaged by genus) of these datasets onto the phylogeny also showed insignificant phylogenetic signal. Aside from homoplasy caused by convergent evolution of skull shape, the massive extinction of lagomorphs after the late Miocene is proposed as one of the main causes for diluting phylogenetic signals in their morphological evolution. Acknowledging the loss of phylogenetic signals in skull shape and supraorbital processes of extant genera sheds new light on the long-standing difficulties for understanding higher-level systematics in Lagomorpha.