Depth-dependent abundance of Midas Cichlid fish (Amphilophus spp.) in two Nicaraguan crater lakes

Abstract

The Midas Cichlid species complex (Amphilophus spp.) in Central America serves as a prominent model system to study sympatric speciation and parallel adaptive radiation, since small arrays of equivalent ecotype morphs have evolved independently in different crater lakes. While the taxonomy and evolutionary history of the different species are well resolved, little is known about basic ecological parameters of Midas Cichlid assemblages. Here, we use a line transect survey to investigate the depth-dependent abundance of Amphilophus spp. along the shores of two Nicaraguan crater lakes, Apoyo and Xiloá. We find a considerable higher density of Midas cichlids in Lake Xiloá as compared to Lake Apoyo, especially at the shallowest depth level. This might be due to the higher eutrophication level of Lake Xiloá and associated differences in food availability, and/or the presence of a greater diversity of niches in that lake. In any case, convergent forms evolved despite noticeable differences in size, age, eutrophication level, and carrying capacity. Further, our data provide abundance and density estimates for Midas Cichlid fish, which serve as baseline for future surveys of these ecosystems and are also relevant to past and future modeling of ecological speciation.

Differential predation on the two colour morphs of Nicaraguan Crater lake Midas cichlid fish: implications for the maintenance of its gold-dark polymorphism

“…For example, water depth might be a relevant factor in the maintenance of the colour polymorphism in Midas cichlids if the relative impact of predators changes along this axis, as it is likely to do. This could be due to changes in the relative impact of birds versus fish predators at different water depth, or due to changes in the relative abundances of colour morphs in Midas cichlids along the water column as the gold morph is more common at greater depths (McKaye & Barlow, ; Elmer et al ., ; Dittmann et al ., ), although Midas cichlids of both morphs are commonly seen foraging at the surface of the water (see Supporting Information). Understanding the role of water depth on predation rate was beyond the scope of the present study, but future research should focus on this and other issues to better understand the interaction of predation and colour polymorphism in Midas cichlid fishes.…”

“…We determined the relative abundance of gold and dark fish in the lake using linear transects following Dittmann et al . (), with the difference that we counted fish at one depth only (average of 7 m). Seven line transects were covered by two SCUBA divers, swimming side by side, both recording the number of dark and gold fish observed.…”

Genomic signatures of divergent selection and speciation patterns in a ‘natural experiment’, the young parallel radiations ofNicaraguan crater lake cichlid fishes

“…However, a parallel difference in depth distribution, with A. astorquii and A. amarillo using the shallow and A. chancho and A. xiloaensis using the deep areas of respective crater lakes has been proposed, (Barluenga & Meyer ; Dittmann et al . ) though not tested.…”

Heterospecific aggression bias towards a rarer colour morph

“…The lake supports more than 10 cichlid species whose breeding seasons are largely overlapping [35][36][37]. Typically, irrespective of species, when pairs are ready to spawn, they claim a territory on the lake floor, and then aggressively defend the territory until the juveniles are ready to disperse [35,38].…”