Effect of different protein supply on growth of three populations of a crab adapted to low energy diets

Abstract

Juvenile individuals of the crab Neohelice granulata (Brachyura: Grapsoidea: Varunidae) were grown in laboratory using five artificial diets containing 3, 6, 12, 18 and 24 % of crude protein and 3 % of lipids during 7 months. Crabs belonged to three different populations. Two of them, San Antonio Oeste (SAO) and Riacho San José (RSJ) are close; they are not genetically differentiated but vary in morphological traits. The third, Mar Chiquita (MC), is far and genetically differentiated from the other two, but morphological traits of their individuals are intermediate. The growth (absolute and relative size change, final body mass), molting frequency, hepatosomatic index of individuals, as well as the Carbon and Nitrogen content and histological structure of their digestive glands, were analyzed. Mar Chiquita individuals differed from one or both of the other two populations. Time to first molt was significantly longer in MC, final size was significantly smaller in MC than RSJ and hepatosomatic index was significantly lower in MC compared to SAO and RSJ. San Antonio Oeste and RSJ individuals never differed. Furthermore, in all cases crabs were able to molt and growth with all diets, although growth in size and mass were higher, and intermolt periods shorter, when diets contained higher percentages of protein. It is concluded that species is well adapted to low quality food sources and it is suggested that size differences previously observed between SAO and RSJ crabs are due to phenotypic plasticity, while differences with MC population are governed by evolutionary adaptation to different food availability.

Inter‐population differences in feeding ecology under nitrogen‐limited diets: Field growth and the role of cannibalism in limiting/improving reserve accumulation

“…Based on our results, we could assume that crabs from all three populations responded similarly to the different conditions prevailing at each site. Nevertheless, in a previous study (Bas et al, ), juvenile N. granulata from the same three populations were reared for 7 months under controlled laboratory conditions at 20°C temperature. Final size (cumulative growth over three molt events) differed between populations of origin for all test diets, although size after every single molt did not.…”

“…Opaque tubes were added as refuges, and water was changed weekly. Each group from both sites was fed daily for two months, with food pellets containing 3% (low content) or 24% (high content) of total protein, 3% lipids, and a proportion of carbohydrates adequate to attain a final energy content of 1,200 kJ/g (see formulation in Bas et al, ). After that time, there were two groups for each population: one with high‐protein diet and another with low protein diet.…”

“…in Bas et al, 2016). After that time, there were two groups for each population: one with high-protein diet and another with low protein diet.…”

“…Previous field studies showed that the food ingested at any given time depends on the combination of physical and biological factors, which varies among populations (Bas et al, ). Most of the natural diet of this species is protein‐deficient, and crabs are able to grow and molt even when their diet contains an extremely low level of N (Bas et al, ; Bas, Luppi, & Spivak, ). Nevertheless, the analysis of the stomach content of natural populations of N. granulata shows that the proportion of crustaceans consumed (mainly congeners) varies among populations (Bas et al, ), and the importance of cannibalism in diets depends on the content of organic matter in the sediment (Mendez Casariego, Montemayor Borsinger, Valiñas, & Luppi, ).…”

“…tioned laboratory experiments with crabs of comparable size,Bas et al (2016) found that crabs from MC grew less and accumulated fewer reserves under any feeding condition when compared to RSJ F I G U R E 5 Frequency of the different behaviors registered (buried, walking, standing activities) related to presence/absence of adults. Observations were performed at each site (MC, SAO and RSJ) for 20 min with and without an adult male as potential predator of local juveniles.…”