V.M. Cubillos

Characterisation of strains of infectious bronchitis virus isolated in Chile

Nine isolates of infectious bronchitis (IB)-like viruses were made from 23 flocks (broilers or layers) in Chile experiencing the types of disease problems commonly associated with IBV. Their identity as IB viruses was confirmed. The histological changes they caused in tracheal organ cultures (OC) are described. Serum neutralisation tests performed in embryonated eggs (alpha-method) suggested that four of the isolates were serologically related to the Massachusetts (Mass) serotype of IBV and one to Connecticut. The four other strains were examined further by a serum neutralisation test in OC (ss-method). One was found to be of the Mass serotype but the others were found to be unrelated antigenically to a wide range of IBV serotypes isolated in many countries over a number of years. One of these three strains and the Mass strain, when given intranasally to 8-day-old specified pathogen free chickens together with pathogenic serotypes of E.coli, caused some mortality and considerable morbidity. The H120 vaccine strain was found not to protect completely against challenge with these four strains 21 days later.

Unusual source of food : impact of dead siblings on encapsulated embryo development of Crepipatella fecunda (Gastropoda: Calyptraeidae)

Embryonic cannibalism has been identified in directly developing calyptraeid species through observation of the ingestion of encapsulated sibling embryos. The object of the present study was to determine the effects of experimentally induced cannibalism on larval development in encapsulated larvae of Crepipatella fecunda (a species having mixed development). The effects studied included the time of intracapsular development, protoconch size and velar characteristics of the larvae. Mortality was induced during intracapsular development through mechanical disruption (‘treatment’) of embryos. A treatment and control group of embryos from the same female were compared. Encapsulated veligers actively fed on their sacrificed congeners. Larvae hatched in less than 10 days from treated capsules and had mean shell lengths and velum areas significantly lower than those from the control, but no significant differences in cilia length. In treated capsules where the embryos underwent a slow development (>20 days), the larvae produced shells, vela and cilia larger than those of the controls. In an intermediate period of intracapsular development, the differences recorded among larval characters were not statistically significant. The results showed that: (1) the encapsulated veligers were capable of feeding on exogenous food before hatching; (2) the consumption of non-living congeners decreased the time of intracapsular development; and (3) the morphometry of the larvae hatching from treated capsules varied depending on the period of intracapsular development and seems to be adaptively stabilised towards homogeneous larval morphometry.

The relationship between UV-irradiance, photoprotective compounds and DNA damage in two intertidal invertebrates with contrasting mobility characteristics

The photoprotective role of mycosporine-like amino acids (MAA) against the generation of DNA cyclobutane pyrimidine dimers (CPD) was studied in the sessile intertidal anemone Actinia tenebrosa and the mobile intertidal gastropod Diloma aethiops through 27months at a mid-latitude New Zealand location. MAA were sequestered by A. tenebrosa and D. aethiops from their diet, although maximum total MAA levels in both species were not correlated with seasonal variation in maximum ambient UV-B levels recorded at the collection site. Temporal changes in total MAA in A. tenebrosa showed a six months lag-time in their concentration regarding to the environmental UV-B levels. This lag period corresponded to an observed increase in CPD production from spring to summer; suggesting that MAA do not completely protect the anemone from UV-B during summer. For D. aethiops, total MAA concentrations did not change significantly during the study, although qualitative changes in MAA were apparent. A month lag-time in MAA concentration in D. aethiops and possibly the physical barrier that the shell confers to the animal, can explain reduced CPD levels in comparative terms with A. tenebrosa. Although MAA are used by invertebrates for photoprotection, contrasting mobility characteristics and the presence of physical adaptations can confer them important protection levels during temporal changes of UV-B at mid-latitude places of the Southern Hemisphere.

Are embryonic developing modes determinant in the acquisition and levels of photoprotective compounds in slipper limpets of the Crepipatella genus

The type of embryonic development (mixed and direct) and its influence on the accumulation and translocation of photoprotective compounds from the mother to the encapsulated embryo was studied in the intertidal gastropods Crepipatella peruviana and Crepipatella dilatata during their reproductive peak. HPLC/MS was used to determine type and levels of sunscreen compounds (total carotenoids; TC/and mycosporine-like amino acid; MAA) in brooding females, capsule walls and early and pre-hatching embryos of both species. Photoprotective compounds were only quantified in nurse eggs of C. dilatata. Our results indicate that females of both species can accumulate TC and MAA at different levels, and they are able to transfer them selectively to capsule walls, embryos and nurse eggs. Palythine-serine (MW=244Da; λmax=320nm) and MAA-330 (MW=234Da; λmax=330nm) constitute total MAA pool in brooding females, whereas brooded embryos incorporate palythine (MW=244Da; λmax=320nm) to the MAA pool. Although TC was transferred from the mother to the embryo through the yolk in both species, MAA trespass showed differences. Females of C. peruviana transfer MAA to their embryos through the embryonic yolk; C. dilatata can transfer MAA only through their nurse eggs, which are consumed by embryos during the terminal stages of intracapsular development. Differences between mixed and direct embryonic development, as well as environmental UV-R levels, which the recently hatched larvae and juveniles of C. peruviana and C. dilatata are exposed to, would determine levels of sunscreen compounds in each species. Higher TC and MAA levels in pre-hatching larvae of C. peruviana compared to C. dilatata, indicate a necessity of C. peruviana for protection against UV-R radiation during approximately 15days when their veliger larvae remain in the water column before metamorphosis is complete. Conversely, low photoprotective levels in pre-hatching juveniles of C. dilatata could be related to low UV-R exposure levels due to the direct incorporation to the benthos and the presence of a protective shell.

Role of the Substrate in Feeding and Growth of the Marine Suspension-Feeding Gastropods Crepidula fornicata and Crepipatella peruviana

Unlike lamellibranch bivalves, suspension-feeding calyptraeid gastropods lack siphons and paired shell valves to regulate water inflow. This study was designed to determine if calyptraeid gastropods use the solid surface to which they attach to facilitate food particle capture. Juveniles of both Crepidula fornicata and Crepipatella peruviana were maintained with phytoplankton for 3 to 6 wk in the laboratory, either attached to solid substrate or without solid substrate. Individuals of C. fornicata and C. peruviana that were reared on solid substrate grew about five to ten times more, or two times more, respectively, than those deprived of solid substrate. Final tissue weights were also significantly greater for individuals of both species that had been reared on solid substrate. For the two species, phytoplankton clearance rates were about two to three times higher for individuals attached to solid substrate than for those without solid substrate; rates of food cord production from the gills were also significantly higher. About 50% of C. peruviana that were deprived of solid substrate died during the first 3 wk of observation, and about 60% were dead by 6 wk. In contrast, most individuals of C. peruviana that were attached to solid substrate survived for the entire 6-wk study period, and all of the C. fornicata survived whether or not they were attached to solid substrate. The solid substrate to which calyptraeid gastropods attach clearly plays an important role in their feeding biology, although the precise role remains to be explored.

Growing Safe: Acute Size Escape from Desiccation in Juvenile Crepipatella peruviana (Mollusca: Gastropoda)

Desiccation is an important limiting factor in the intertidal zone. Generally decreasing seaward, desiccation stress can also be alleviated in wet microhabitats. Juvenile snails are generally more susceptible to desiccation than adults, and, for some species, juveniles must therefore hide in microhabitats to survive emersion. The transition from hiding in safe microhabitats to being able to survive fully exposed for the duration of low tide is not well documented. In this study, we investigated the influence of size on desiccation tolerance in juveniles of the calyptraeid gastropod Crepipatella peruviana to determine the size at which they can first survive exposure to air. Juveniles 2–13 mm long were exposed to 75% or 100% relative humidity for 0.5–6.5 hours. Juveniles smaller than 5 mm in shell length did not survive emersion at 75% relative humidity for even 0.5 hours; surprisingly, most also perished after short exposures to air at 100% relative humidity, suggesting that something other than desiccation stress may also be at play. In marked contrast, 82% of juveniles larger than 6 mm in shell length survived exposure to 75% relative humidity for the full 6.5 hours. In a field survey, no juveniles smaller than 9 mm were found on exposed rock but rather were found only in wet microhabitats. We suggest that the clearly defined size escape from desiccation may reflect a change in gill functioning or a newfound ability to retain water more effectively within the mantle cavity at low tide.