Abstract
Paralomis granulosa Jacquinot is a commercially fished lithodid crab species living in subantarctic and cold-temperate regions of southern South America. Its larval stages (Zoea I, II, Megalopa) are fully lecithotrophic, developing in the complete absence of food from hatching through metamorphosis; first feeding occurs in the first juvenile crab stage. In laboratory rearing experiments conducted at constant 1, 3, 6, 9, 12, and 15°C, we studied rates of larval and early juve- nile survival and development in relation to temperature. At 1°C, many larvae (52%) reached the Megalopa stage almost 2 mo after hatching, but all died subsequently without passing through meta- morphosis. Larval development was successfully completed at all other temperatures, with maximum survival at 6 to 9°C. The time of non-feeding larval development from hatching to metamorphosis lasted, on average, from 24 d (at 15°C) to almost 4 mo (117 d, at 3°C). When the experiment was ter- minated 1 yr after hatching, the 3rd (3°C) to 8th (15°C) juvenile crab instar had been reached. The relationship between the time of development through individual larval or juvenile stages (y) and temperature (T) was described as a power function (y = a × T b , or log(y) = log(a) + b · log(T); the same regression model was also used to describe the temperature-dependence of cumulative periods of development from hatching. The wide thermal tolerance window for successful larval development (at least 3 to 15°C) and the broad geographic range of this species show that the early life-cycle stages of P. granulosa are cold-eurythermal. This physiological trait together with larval independence of food indicate that this lithodid crab species is well adapted to severe conditions of cold in com- bination with the food-limitation in subantarctic regions. Since similar traits have been also observed in other Lithodidae, we suggest that early life-history adaptations to low temperatures and low plank- tonic productivity may explain the high number of lithodid species occurring at high latitudes and in the deep sea, i.e. in conditions under which other Decapoda show strongly reduced diversity.
Highlights
A macroecological pattern in the geographical distribution of higher animal and plant taxa is a decreasing trend in species diversity from low latitudes towards the poles
At the lowest temperature (1°C, tested only for Hatch A), 52% of the larvae survived through the 2 zoeal stages, but none of the survivors reached metamorphosis; i.e. complete mortality occurred at the Megalopa stage
Perhaps the most striking result of this study is the wide range of temperatures tolerated by larval and early juvenile stone Paralomis granulosa
Summary
A macroecological pattern in the geographical distribution of higher animal and plant taxa is a decreasing trend in species diversity from low latitudes towards the poles (for recent review of the literature, examples, and discussion of relevant theories see Chown et al.2000). In a recent review of the distribution and life histories of temperate and antiboreal Decapoda of the SW Atlantic Ocean, Spivak (1997) listed a total of 243 species reported from the South. In another biogeographical review for the entire antiboreal region south of ~42° S (including the southern parts of the Atlantic, Pacific and Indian Oceans) Gorny (1999) listed 132 decapod crustacean species, with only 12 (9%) of these occurring south of the Antarctic Convergence. The impoverishment of the Antarctic decapod fauna during periods of climate cooling, about 20 million yr ago, is well documented in the fossil record (Clarke 1993, Crame 1999, Stilwell & Feldmann 2000), indicating that declining temperatures and/or associated factors such as low productivity were critical factors in this process
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