Revista Chilena de Historia Natural 79 (2): 155-167, 2006
RESEARCH ARTICLE
The effects of temperature and oxygen availability on intracapsulardevelopment of
Acanthina monodon (Gastropoda: Muricidae)
Freshwater and marine organisms show similar models of parental care and are faced
with similar constraints to brood, which suggest that comparable environmental limits drive the evolution of parental care in aquatic
systems. In fact, the low diffusion coefficient and solubility of oxygen in aquatic environments affect oxygen acquisition and therefore
the capacity to aggregate embryos. The effect of other critical environmental variables, such as temperature, is less clear. We
assessed the effects of temperature and oxygen availability on (1) the number of developed and undeveloped encapsulated embryos,
(2) the proportion of embryos reaching advanced stages during intracapsular development (counting not only developed and
undeveloped embryos but also abnormal embryos), (3) asynchrony in development (estimated only in capsules in which development
occurred), and (4) final embryo size, as the first step toward identifying the main factors constraining parental care in the ocean. We
used the gastropod Acanthina monodon as a model because it has an extended latitudinal range of distribution and
exhibits feeding larvae during intracapsular development. The latter factor is relevant because previous studies have suggested that
sibling cannibalism could be triggered by intracapsular competition for oxygen. Freshly laid egg capsules were collected and incubated
until embryos hatched under different experimental temperatures (7, 11, 15 and 19 °C) and oxygen conditions (hypoxia: 50-60 % air
saturation; normoxia; and hyperoxia: 150-160 %). More embryos remained in early stages at the end of the experimental period under
hypoxia and at the highest experimental temperature. The mean number of developed embryos was significantly lower under hypoxia
conditions than under normoxia and hyperoxia, but was not influenced by temperature. However, temperature negatively
affected embryo size of developed embryos and the level of asynchrony (number of different developmental stages per capsule). This
suggests that even when a comparable number of embryos develops at high temperature, subsequent survival may be affected, since
developed embryos attained smaller sizes. The negative effect of high temperature on embryo aggregation has also been reported for
Brachyuran crabs, affecting female patterns of oxygen provision and brooding costs. This evidence suggests that aggregating embryos
in the ocean, even under optimum oxygen conditions, may be negatively affected at high temperatures. Spatial patterns of distribution
of brooding species in the ocean tend to agree with this prediction. Our analysis is particularly relevant given the current increase in
temperature and the proportion of anoxic areas in the world’s oceans.
Key words:
brooding, intracapsular
development, gastropods, oxygen, temperature
