Transitions in functional morphology from "large branchiopods" to Cladocera: Video and confocal microscopic studies of Cyclestheria hislopi (Cyclestherida) and Sida crystallina (Cladocera: Ctenopoda).

Great diversity is found in morphology and functionality of arthropod appendages, both along the body axis of individual animals and between different life-cycle stages. Despite many branchiopod crustaceans being well known for displaying a relatively simple arrangement of many serially post-maxillary appendages (trunk limbs), this taxon also shows an often unappreciated large variation in appendage morphology. Diplostracan branchiopods exhibit generally a division of labor into locomotory antennae and feeding/filtratory post-maxillary appendages (trunk limbs). We here study the functionality and morphology of the swimming antennae and feeding appendages in clam shrimps and cladocerans and analyze the findings in an evolutionary context (e.g., possible progenetic origin of Cladocera). We focus on Cyclestheria hislopi (Cyclestherida), sister species to Cladocera and exhibiting many "large" branchiopod characters (e.g., many serially similar appendages), and Sida crystallina (Cladocera, Ctenopoda), which likely exhibits plesiomorphic cladoceran traits (e.g., six pairs of serially similar appendages). We combine (semi-)high-speed recordings of behavior with confocal laser scanning microscopy analyses of musculature to infer functionality and homologies of locomotory and filtratory appendages in the two groups. Our morphological study shows that the musculature in all trunk limbs (irrespective of limb size) of both C. hislopi and S. crystallina comprises overall similar muscle groups in largely corresponding arrangements. Some differences between C. hislopi and S. crystallina, such as fewer trunk limbs and antennal segments in the latter, may reflect a progenetic origin of Cladocera. Other differences seem related to the appearance of a specialized type of swimming and feeding in Cladocera, where the anterior locomotory system (antennae) and the posterior feeding system (trunk limbs) have become fully separated functionally from each other. This separation is likely one explanation for the omnipresence of cladocerans, which have conquered both freshwater and marine free water masses and a number of other habitats.

Differential mapping of the free barbed and pointed ends of actin filaments in cells.

The actin cytoskeleton plays a pivotal role in many cellular processes. Detailed analysis of the architecture of cellular actin networks provides valuable insight into the dynamic self-organization underlying these processes. In particular, since most of the actin turnover occurs at the tips of actin filaments, it is insightful to map the distribution of filament ends. Here we report a method for differentially labeling the pointed and the barbed ends of actin filaments in cellular networks by permeabilizing cells, following a brief fixation, and introducing labeled actin monomers in the presence or absence of capping protein, respectively. This method quantitatively maps the distributions of free barbed ends and free pointed ends in adherent cells, providing information on the polarity of cytoskeletal structures and mapping active sites available for actin assembly or disassembly. We demonstrate the use of this method by mapping the distribution of actin filament ends in motile fish epithelial keratocytes and in several mammalian cell lines, and show that free barbed ends are enriched near the tip of protruding lamellipodia while free pointed ends concentrate toward the rear.