A histological survey of avian post-natal skeletal ontogeny

Bone histology of crown-group birds is a research topic of great interest, permitting insight into the evolution of remarkably high growth rates in this clade and variation across the altricial-precocial spectrum. In this study, we describe microanatomical characteristics of the humerus and femur in partial growth series from 14 crown group birds representing ten major clades (Struthioniformes, Galliformes, Apodiformes, Columbiformes, Charadriiformes, Accipitriformes, Strigiformes, Psittaciformes, Falconiformes, and Passeriformes). Our goals were to: (1) describe the microanatomy of each individual; (2) make inter-and intra-taxonomic comparisons; (3) assess patterns that correspond with developmental mode; and (4) to further parse out phylogenetic, developmental, and functional constraints on avian osteological development. Across taxa, the femoral and humeral tissue of neonates can be broadly characterized as highly-vascularized, disorganized woven bone with great variation in cortical thickness (inter-and intrataxonomically, within an individual specimen, and within a single section). The tissue of precocial chicks is relatively more mature at hatching than in altricial, but other categories along the developmental spectrum were less easy to distinguish, thus we were unable to identify a definitive histological proxy for developmental mode. We did not find evidence to support hypotheses that precocial chicks exclusively have thicker cortices and more mature bone in the femur than the humerus at time of hatching; instead, this is a characteristic of nearly all taxa (regardless of developmental mode), suggesting deep evolutionary origins and the effects of developmental channeling. Bone tissue in adults exhibited unexpected variation, corresponding to differences in body size. Large-bodied birds have cortices of fibrolamellar bone, but organization of tissue increases and vascularity decreases with diminishing body size. The outer circumferential layer (OCL) also appears at earlier growth stages in small-bodied taxa. Thus, while the OCL is indicative of a cessation of appositional growth it is not always indicative of cortical maturity (that is, maximum organization of bony tissue for a given taxon). Small size is achieved by truncating the period of fast growth; manipulation of the timing of offset of bone growth is therefore an important factor in changing growth trajectories to alter adult body size.

Natural History and Reproductive Data of Kurixalus yangi (Anura: Rhacophoridae) in Nagaland, India

The genus Kurixalus Ye, Fei et Dubois, 1999 (Rhacophoridae Hoffman, 1932) is a small and taxonomically difficult group of treefrogs for which biological and reproductive data are missing for most of the species. A recent study of the K. odontotarsus species group (Yu et al., 2017a) revealed numerous undescribed lineages. Among them a lineage comprising specimens from Myanmar and western Yunnan, China was described as K. yangi. We report here the presence of a population of this species from Nagaland, North East India, identified by DNA barcoding of the 16S rRNA gene and morphology. A pair of adults found in amplexus is described morphologically. Data on reproduction and developmental mode were until now unknown for the continental species of this genus. Observation of reproduction in the field of K. yangi from Nagaland provided us data on its reproductive activity including spawning behavior and reproductive mode, and details on the larval developmental timing. The tadpole of this species is described for the first time including buccal anatomy. Adults are commonly found in the stumps of bamboo internodes. They breed in forest ponds, temporary rain pools or rain water tanks. Breeding activity starts from mid-April till late part of July. Unpigmented eggs measure 2.4 – 2.7 mm and are laid underwater. Under natural conditions (air temperature 18 – 30°C, water temperature 12 – 24°C), the frog complete its larval life cycle in 47 days. The tadpole shows a «classical» pond-dwelling morphology and reproductive mode. These reproductive data are compared to the Taiwanese species for which the developmental mode is well known and the evolution of the reproductive modes within the genus is discussed.

Plasticity and Artificial Selection for Developmental Mode in a Poecilogonous Sea Slug

Developmental mode describes the means by which larvae are provisioned with the nutrients they need to proceed through development and typically results in a trade-off between offspring size and number. The sacoglossan sea slug Alderia willowi exhibits intraspecific variation for developmental mode (= poecilogony) that is environmentally modulated with populations producing more yolk-feeding (lecithotrophic) larvae during the summer, and more planktonic feeding (planktotrophic) larvae in the winter. I found significant family level variation in the reaction norms between 17 maternal families of A. willowi when reared in low (16 ppt) versus high (32 ppt) salinity. I documented a significant response to selection for lecithotrophic larvae, the proportion of which increased 32% after three generations of selection in high salinity, and 18% after 2 generations in low salinity (realized heritability: 0.365 ± 0.024). The slope of the reaction norm was maintained following one generation of selection for lecithotrophy and one generation of selfing. The rapid response to selection favoring one developmental mode may speak to the rarity of intraspecific variation for developmental mode, which could fix for one mode over another much more readily than has generally been assumed from studies of less plastic organisms.

Size and shape of eggs of Neognathae: effects of developmental mode and phylogeny

We evaluated the variation in absolute size and shape of birds’ eggs and the effects of developmental mode and phylogenetic relatedness on these traits. Eggs were characterized by length, diameter, and three indices of egg shape. Indices of egg shape were calculated as the ratio of radii that described the curvature of pointed end (cloacal zone), blunt end (infundibular zone), and lateral zone to egg diameter. We found that eggs shape was less variable than the absolute size of eggs. Index of the cloacal zone was the most changeable and index of the infundibular zone was very conservative. Size and shape of eggs could be better explained with phylogenetic relatedness than developmental mode.