Marta Linde

Weight-length relationships of littoral to lower slope fishes from the western Mediterranean

Weight–length relationships (WLRs) are presented for 103 fish species inhabiting littoral to lower slope habitats of the Balearic Islands and the Iberian coast (western Mediterranean). Samples were collected using seven types of fishing gear and at depths ranging from 0.5 to 1713 m. Captures were made between the years 1991 and 2001. The b values in the WLR W = aL b varied between 2.072 and 3.847 and showed a mean value of 3.03 (S.E. =± 0.03). Whenever possible, the b values for the species obtained both in this study and some of the previously reported in the Mediterranean Sea were compared, showing the existence of spatial variation whose causes are discussed.

Differential correlates of diet and phylogeny on the shape of the premaxilla and anterior tooth in sparid fishes (Perciformes: Sparidae)

We explore the correlational patterns of diet and phylogeny on the shape of the premaxilla and anterior tooth in sparid fishes (Perciformes: Sparidae) from the western Mediterranean Sea. The premaxilla is less variable, and in spite of the presence of species‐specific features, a common structural pattern is easily recognizable in all species (i.e. the ascending and the articular processes are fused in a single branch, as in many percoid fishes). In contrast, tooth shape is more variable, and different structural types can be recognized (e.g. canine‐like or incisive). Coupling geometric morphometric and comparative methods we found that the relationship between shape, diet and phylogeny also differs between premaxilla and tooth. Thus, the shape of the premaxilla is significantly correlated with food type, whereas the shape of the teeth is not correlated with diet, and probably reflects the species phylogenetic relationships. Two biological roles, resistance against compressive forces generated in the buccal cavity and the size of the oral gape, would explain the ecomorphological patterns of the premaxilla. The premaxilla and anterior tooth appear to evolve at different rates (mosaic evolution) and represent an example of morphological traits belonging to the same functional unit but following uncoupled evolutionary pathways.

Testing Allsop and West’s size at sex change invariant within a fish species: a spurious ratio or a useful group descriptor?

Recently, it has been suggested that sequential hermaphrodites, from a variety of taxa and a wide range of sizes, change sex at the same relative size. It is said that there exists an invariant (a constant ratio) for such a life trait. However, recent criticisms point out that these results could be a statistical artefact. It has been argued that the wider the range of x‐axis values (from 2 mm to 1.5 m in the case of sex change), the higher the probability of identifying an invariant by chance. Here, the invariance of the size at sex change ratio is analysed within a single fish species for which the size of sex change varies within a range of only 6.5 cm. Our results support the invariant rule that fishes change sex when reaching 79% of their maximum size.

Why protogynous hermaphrodite males are relatively larger than females? Testing growth hypotheses in Mediterranean rainbow wrasse Coris julis (Linnaeus, 1758)

Several growth hypotheses have been tested to investigate why males of the sequential hermaphrodite, Mediterranean rainbow wrasse, Coris julis (Linnaeus, 1758), are relatively larger than females of the same age. Individual growth trajectories were estimated to test these hypotheses. A good linear relationship between otolith size and body size was observed (r2 = 0.71, n = 609), thus, past somatic growth of any specific fish can be inferred from the longitudinal data described by the width of annual increments in the otolith. These data were successfully analyzed by a non-linear mixed-effect model (von Bertalanffy growth model) using a Bayesian approach. The results obtained suggest that Mediterranean rainbow wrasse secondary males are relatively larger than females because 1) fish that change sex are already the larger individuals in their age group (specifically those with higher growth rate, ksecondary males = 0.199 and kfemales = 0.161) and 2) they experience a growth spurt after sex change. The differences in growth observed in this species and in other protogynous hermaphrodites could be related to differences in social organization, which, in turn, are related to differences in the sex change mechanisms.