Spatial Models of Abundance and Habitat Preferences of Commerson’s and Peale’s Dolphin in Southern Patagonian Waters

Funding: This research was possible with the support of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Funding for travel to and accommodation for NAD in Aberdeen, Scotland was provided by CONICET and Cetacean Society International. The work of NAD was part of a postdoctoral fellowship funded by CONICET. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Characterisation of the vascular pathology in Sigmodon hispidus (Rodentia: Cricetidae) following experimental infection with Angiostrongylus costaricensis (Nematoda: Metastrongylidae)

BACKGROUND Angiostrongylus costaricensis is a nematode that causes human abdominal angiostrongyliasis, a disease found mainly in Latin American countries and particularly in Brazil and Costa Rica. Its life cycle involves exploitation of both invertebrate and vertebrate hosts. Its natural reservoir is a vertebrate host, the cotton rat Sigmodon hispidus. The adult worms live in the ileo-colic branches of the upper mesenteric artery of S. hispidus, causing periarteritis. However, there is a lack of data on the development of vasculitis in the course of infection. OBJECTIVE To describe the histopathology of vascular lesions in S. hispidus following infection with A. costaricensis. METHODS Twenty-one S. hispidus were euthanised at 30, 50, 90 and 114 days post-infection (dpi), and guts and mesentery (including the cecal artery) were collected. Tissues were fixed in Carson’s Millonig formalin, histologically processed for paraffin embedding, sectioned with a rotary microtome, and stained with hematoxylin-eosin, resorcin-fuchsin, Perls, Sirius Red (pH = 10.2), Congo Red, and Azan trichrome for brightfield microscopy analysis. FINDINGS At 30 and 50 dpi, live eggs and larvae were present inside the vasa vasorum of the cecal artery, leading to eosinophil infiltrates throughout the vessel adventitia and promoting centripetal vasculitis with disruption of the elastic layers. Disease severity increased at 90 and 114 dpi, when many worms had died and the intensity of the vascular lesions was greatest, with intimal alterations, thrombus formation, iron accumulation, and atherosclerosis. CONCLUSION In addition to abdominal angiostrongyliasis, our data suggest that this model could be very useful for autoimune vasculitis and atherosclerosis studies

Habitat of Argentine squid (Illex argentinus) paralarvae in the southwestern Atlantic

Illex argentinus is one of Argentina’s most important commercial species and sustains one of the most important cephalopod fisheries worldwide. Catches, and presumably population abundances, show strong interannual fluctuations, probably forced by processes which occur during the species’ early life history. However, knowledge of paralarvae ecology and the influence of the environment on larval survival are fragmentary and limited. In this work, we describe the habitat of I. argentinus paralarvae caught in 4 research cruises between 34° and 42°S, taking into account information on seasonal transport of paralarvae by currents, chlorophyll a concentrations, characteristics of water masses and water column structure. Argentine squid paralarvae habitat is environmentally complex. Paralarvae occur in the plankton when the biological production in the area is relatively low but offshore transport is at a minimum, thus decreasing the chances of the paralarvae being exported to places unsuitable for survival. We discuss how the synchronization of the squid reproductive cycle relates to these environmental events and may improve paralarvae survival and recruitment.</jats:p

Distribution and behavior of Argentine hake larvae: Evidence of a biophysical mechanism for self-recruitment in northern Patagonian shelf waters

It has been proposed that vertical movements of planktonic organisms coupled to a horizontally or vertically stratified circulation pattern could describe a retention mechanism, with ecological advantages such as favoring recruitment success. The Patagonian stock of the Argentine hake Merluccius hubbsi spawns mainly from January to February in relation to a highly productive tidal frontal system. Although retention of fish eggs and larvae has been previously hypothesized for this system, it has not been fully proven and its mechanisms have not yet been proposed for hake early stages. To better understand the physical and biological processes involved in the survival and distribution of hake larvae, we focused on transport features and associated larval behavior governing the retention of larvae in the spawning area and their subsequent distribution to settlement and nursery grounds. To test this hypothesis at appropriate spatial and temporal scales, we analyzed acoustic records to describe vertical and horizontal distribution patterns of hake larvae, discrete plankton samples to confirm the identity of acoustic targets, and outputs from a numerical circulation model to estimate current patterns in the region during the hake spawning months. Coinciding with the development of a functional swimbladder, hake larvae of 4 mm and larger showed a strong vertical distribution pattern associated with a sound scattering layer migrating from the thermocline during the night to near-bottom depths during the day. This diel vertical migration pattern was associated with the circulation structure, equivalent to a two-layer flow, indicating a recirculation pattern in the vertical plane. The retention of early larval stages in the spawning area was evident from the acoustic data, indicating a persistent location for the bulk of hake larvae at the main spawning ground during summer months. The distribution extends to the rest of the nursery grounds as the breeding season advances in agreement with the general pattern of middle shelf bottom circulation vectors produced by the numerical model. The results are discussed within the framework of Bakun’s fundamental triad, identifying its elements. In addition, a conceptual model for the main biophysical coupling processes during the early life history of M. hubbsi is proposed in order to gain insight about the recruitment mechanism of this species.

Absonifibula estuarina sp. n. (Monogenea: Diclidophoridae) parasite of juvenile Cynoscion guatucupa (Osteichthyes) from southwestern Atlantic Ocean

Absonifibula estuarina sp. n. (Diclidophoridae, Absonifibulinae), is described from the gills of juvenile striped weakfish, Cynoscion guatucupa (Cuvier), from the southwestern Atlantic, Argentinean coast. This marine fish migrates to estuarine areas to spawn where exclusively juveniles are found parasitized; adult fish in marine water were never found to be parasitized by this monogenean. A. estuarina sp. n. is characterized mainly by the pedunculate clamps dissimilar in size, the shape of anterior jaw with sclerite 'a' attached to a sub-trapezoidal lamellate extension and fused to sclerites 'c' and 'd'. It differs from Absonifibula bychowskyi Lawler & Overstreet, 1976, the only known species of the genus, in the shape and arrangement of the genital corona, which is armed with six similar hooks disposed in circle and the sub-trapezoidal shape of lamellate extension ('b'). The restriction to juvenile sciaenids is a shared feature among the Absonifibulinae indicating an estuary-dependent life cycle