Trophic polymorphism, habitat and diet segregation in Percichthys trucha (Pisces: Percichthyidae) in the Andes

Abstract

Divergent natural selection affecting specific trait combinations that lead to greater efficiency in resource exploitation is believed to be a major mechanism leading to trophic polymorphism and adaptive radiation, We present evidence of trophic polymorphism involving two benthic morphs within Percichthys twhu, a fish endemic to temperate South America. In a series of lakes located in the southern Andes, we found two morphs of R hucha that could be distinguished on the basis of gill raker length and five other morphological measures, most of which are likely associated with the use of food resources. The differences were consistent across all lakes examined, and were correlated with habitat use and diet. Individuals with longer gdl rakers were more abundant in the littoral zone (littoral morph) while the short gill-raker morph was more abundant at 10 m depth and deeper (deep benthic morph). Both morphs fed primarily on benthic invertebrates, but the littoral morph fed more on larval Anisoptera than did the deep benthic morph. Phenotypic correlations among traits were high for the littoral morph, but low and non-significant for the deep-benthic morph. We suggest that gill raker length may influence the relative efficiency of suction feeding for the two morphs. This is the first evidence of trophic polymorphism in fishes from temperate South America. 0 IYY8 The Linnean Society or London ADDITIONAL, KEY WORDS:-trophic morphology -gill raker -competitive divergence -habitat use -endemics -Patagonia.

Is the decline of birds and amphibians in a steppe lake of northern Patagonia a consequence of limnological changes following fish introduction?

“…P. colhuapiensis and a few O. mykiss were captured in Laguna Blanca, with the highest captures of P. colhuapiensis in the littoral zone. The abundances recorded for P. colhuapiensis in Laguna Blanca are the highest, in comparison with other populations of P. colhuapiensis and P. trucha, in Patagonian lakes and reservoirs surveyed with comparable fish gear Ruzzante et al, 1998Ruzzante et al, , 2003Buria, 2001;Aigo, 2002;Milano et al, 2002). The extremely high abundance of Percichthys in Laguna Blanca agrees with, and even exceeds, the prediction of Quiro´s (1991) concerning the relationship between the abundance of salmonids and Percichthys, and temperature ( Figure 5).…”

“…Nowadays, water transparency is markedly lower in Laguna Blanca compared with previous data (4-5 m in Daciuk (1968) and in ), and present values (41 m) are lower than those obtained in fishless lakes (Table 1). Both P. colhuapiensis and P. trucha are benthivorous fish Ruzzante et al, 1998Ruzzante et al, , 2003Logan et al, 2000) with affinities for eating detritus in the case of P. trucha (Ruzzante et al, 2003) and for macrozoobenthos and fish in P. colhuapiensis Macchi et al, 1999). This paper reports preliminary data that are perhaps useful in the design and evaluation of possible restoration programmes.…”

Fishes of southern South America: a story driven by temperature

“…Such lakes tend to have few species, partly because there has been little time or opportunity for colonization and partly because there has been even less time for in situ speciation to have occurred. Consequently, the organisms that do colonize these lakes are likely to encounter under-or unexploited resources and few competitors (see Ruzzante et al 1998 for a review).…”

Spatial and temporal distribution of landlockedGalaxias maculatusandGalaxias platei(Pisces: Galaxiidae) in a lake in the South American Andes

“…The original measurements were transformed to base 10 logarithms to obtain approximate linear relationships, and corrected for standard length according to: AM = OML -(RC x (log SL -mean (log SL))) (1) following Battini et al (1995), Cussac et al (1998), and Ruzzante et al (1998) where AM = adjusted measurement, OML = original measurement logarithm, RC = regression coefficient between the logarithm of the character and the logarithm of SL, mean (log SL) = overall mean of SL logarithm. This approach was preferred to the classical ratio between morphological measurements to avoid sizedependent changes of these ratios as a consequence of the allometric relationships expressed by the regression coefficient (RC) between the logarithm of the character and the logarithm of SL.…”