Evolutionary expansion of the Monogenea

The evolutionary expansion of the monogeneans has taken place in parallel with the diversification of the fish-like vertebrates. In this article the main trends in monogenean evolution are traced from a hypothetical skin-parasitic ancestor on early vertebrates. Special consideration is given to the following topics: early divergence between skin feeders and blood feeders; diversification and specialization of the haptor for attachment to skin; transfer from host to host, viviparity and the success of the gyrodactylids; predation on skin parasites and camouflage; colonization of the buccal and branchial cavities; diversification and specialization of the haptor for attachment to the gills; phoresy in gill parasites; the development of endoparasitism and the origin of the cestodes; the success of dactylogyroidean gill parasites; the uniqueness of the polyopisthocotyleans; ovoviviparity and the colonization of the tetrapods. Host specificity has been the guiding force of coevolution between monogeneans and their vertebrate hosts, but the establishment of monogeneans on unrelated hosts sharing the same environment (host-switching) may have been underestimated. Host-switching has provided significant opportunities for evolutionary change of direction and is probably responsible for the establishment of monogeneans on cephalopod molluscs, on the hippopotamus and possibly on chelonians. There are indications that host-switching may be more common in monogeneans that spread by direct transfer of adults/juveniles from host to host. A limitation on the further expansion of monogeneans is the need for water for the dispersal of the infective larva (oncomiracidium).     

INVESTIGATING THE BIASES IN THE USE OF HARD PREY REMAINS TO IDENTIFY DIET COMPOSITION USING ANTARCTIC FUR SEALS (ARCTOCEPHALUS GAZELLA) IN CAPTIVE FEEDING TRIALS

The analysis of pinniped scats has been used to quantify their diet, using prey remains to identify species and to estimate the numbers and sizes of prey consumed. There are, however, potential biases involved with scat analysis and, for this method to be used successfully, these biases need to be quantified. Thirty-six Antarctic fur seals ( Arctocephalus gazella ) were fed meals of exclusively either fish, squid, or krill and their scats were collected and analyzed. The major sources of error in the analysis of prey remains from scats were the differential erosion and passage rate of items in relation to their size. However, using simple correction functions, such as those which model otolith erosion, it is possible to reduce these errors. Using plastic beads as dietary markers showed recovery rates were negatively related to their size. Larger squid beaks had lower recovery rates than smaller beaks, but there was no size-related bias in the recovery rates of krill carapaces. Only 33% of the squid beaks and 27% of the otoliths originally fed were recovered from the scats. Recovery rates were greater for squid (77%) and fish (50%) eye lenses and these structures gave a better estimate of numbers eaten. Differences found between experimentally derived and published regression equations (used to calculate prey sizes eaten from prey remains) highlights the need for regression equations based on local prey characteristics, if these are to be used with any success to describe the prey eaten.     

NAUTILOIDS WITH MULTIPLE PAIRED MUSCLE SCARS FROM LOWER–MIDDLE ORDOVICIAN OF BALTOSCANDIA

Abstract:  The number, outline and arrangement of muscle scars on the internal mould of the body chamber of five species of Early and Middle Ordovician nautiloids from Baltoscandia are described. The ellesmeroceratids Oelandoceras haelluddenense Foerste and Pictetoceras oliviae King have 9–10 pairs of muscle scars. The oncoceratid Phtanoncoceras ellipticum (Lossen), and Botellusoceras torpense gen. et sp. nov., order and family indeterminate, have eight and nine pairs of muscle scars, respectively. The tarphycerid Estonioceras imperfectum (Quenstedt) has four pairs of muscle scars.     

Embryonic exposure to predator odour modulates visual lateralization in cuttlefish

Predation pressure acts on the behaviour and morphology of prey species. In fish, the degree of lateralization varies between high- and low-predation populations. While lateralization appears to be widespread in invertebrates, we do not know whether heredity and early experience interact during development as in vertebrates. Here we show, for the first time, that an exposure to predator odour prior to hatching modulates visual lateralization in newly hatched cuttlefish. Only cuttlefish that have been exposed to predator odour display a left-turning bias when tested with blank seawater in a T-shaped apparatus. Exposure to predator odour all the incubation long could appear as an acute predictor of a high-predation surrounding environment. In addition, cuttlefish of all groups display a left-turning preference when tested with predator odour in the apparatus. This suggests the ability of cuttlefish to innately recognize predator odour. To our knowledge, this is the first clear demonstration that lateralization is vulnerable to ecological challenges encountered during embryonic life, and that environmental stimulation of the embryo through the olfactory system could influence the development of subsequent visual lateralization.     

Nautiloid debris oriented by long-shore currents along a late Ordovician-early Silurian rocky shore

Siphuncular fragments from arminocerid cephalopods are abundant along 350 m of a well defined rocky shore of late Ordovician or early Silurian age exposed near Churchill in northeastern Manitoba, Canada. The paleoshore is composed of the Precambrian Churchill Quartzite, which is dramatically abutted by carbonate strata gently dipping north beneath Hudson Bay. At one end of the exposure, a former sea stack or sea arch extends prominently outward for 15 m perpendicular to the otherwise linear paleoshore. Probably it acted as a natural groin with some influence on local currents and waves. The orientations of 189 siphuncular fragments were recorded and found to be dominantly perpendicular to the trend of the ancient shore. They are far more cylindrical in shape than conical, and are interpreted to have been rolled to their final resting place pushed by long-shore currents. Concentration of nearly 80% of the fragments towards one end of the shore is consistent with transport by long-shore currents. Ripple marks preserved at a different stratigraphic level form a 45-degree angle to the trend of the paleoshore, providing additional evidence that wave trains must have set up long-shore currents from time to time.     

Further fossil cephalopods from Jamaica

Fossil cephalopods are rare in the Antillean region. A deformed conch of a kossmaticeratid ammonite,Pseudokossmaticerasl sp., from the Maastrichtian of the Blue Mountain Inlier is the first ammonite from southeastern Jamaica. This tentative systematic assignment is in agreement with the age otherwise assigned to these rocks.Cimomia sp. cf.C. vaughani (Gardner) is a hercoglossid nautiloid from the Lower-Middle Eocene Chapelton Formation of western central Jamaica. This is only the fourth nautiloid from this unit; all previous records were ofHercoglossa sp. The specimen is unusual amongst Antillean fossil cephalopods in including the sponge boringEntobia isp., probably indicating a period of post-mortem residence on the sea floor.      

Epigenetics across the evolutionary tree: New paradigms from non-model animals

All animals have evolved solutions to manage their genomes, enabling the efficient organization of meters of DNA strands in the nucleus and allowing for nuanced regulation of gene expression while keeping transposable elements suppressed. Epigenetic modifications are central to accomplishing all these. Recent advances in sequencing technologies and the development of techniques that profile epigenetic marks and chromatin accessibility using reagents that can be used in any species has catapulted epigenomic studies in diverse animal species, shedding light on the multitude of epigenomic mechanisms utilized across the evolutionary tree. Now, comparative epigenomics is a rapidly growing field that is uncovering mechanistic aspects of epigenetic modifications and chromatin organization in non-model invertebrates, ranging from octopus to sponges. This review puts recent discoveries in the epigenetics of non-model invertebrates in historical context, and describes new insight into the patterning and functions of DNA methylation and other highly conserved epigenetic modifications.