Alternative egg-feeding tactics in Telmatherina sarasinorum, a trophic specialist of Lake Matano’s evolving sailfin silversides fish radiation

Abstract

Feeding specialisation is a typical feature of adaptive animal radiations. Different kinds of feeding specialisations have evolved in the endemic sailfin silversides species flock in Lake Matano (Central Sulawesi, Indonesia), including egg-feeding. The present study focuses on Telmatherina sarasinorum, a sailfin silverside species feeding on the eggs of related Telmatherina antoniae. Stomach content analyses supported T. antoniae eggs to be the dominant food item, independent of daytime. We hypothesized that the egg-feeders use alternative tactics for maximising egg consumption under varying densities of both, spawning T. antoniae pairs and competing conspecific egg-feeders. Focal behavioural observations were applied to describe different feeding tactics and to analyse feeding success and the related costs in terms of competitive interactions. Egg-feeders followed single courting pairs of T. antoniae or, alternatively, they switched between different spawning pairs. Following-behaviour, covering one or more spawning events of the host species, was positively related to enhanced egg consumption. Compared to feeding by switching frequently among different spawning pairs, the following tactic came at the cost of likewise increased competition. Behavioural observations suggest that some males monopolize courting pairs of T. antoniae and gain increased amounts of eggs compared to others avoiding competition by switching among pairs. The present results confirm that egg-feeding is a distinct trophic specialisation in T. sarasinorum and increase the scale of behavioural specialisation in Lake Matano's evolving Telmatherina radiation.

Rugged adaptive landscapes shape a complex, sympatric radiation

“…Assortative mating has been reported from most of Lake Matano's Telmatherina species, including three of the five sharpfins (T. sarasinorum, T. wahjui, T. sp. 'thicklip'; see [21,22,27,24]). Together with significant differences in habitat use (figure 1; electronic supplementary material, figure S3), genetic population structure and assortative mating provide strong arguments to reject the hypothesis of only one hypervariable species, and are in agreement with very similar patterns reported from its sister clade, Lake Matano's 'roundfins' [25].…”

“…Quality of DNA was checked on 1% agarose gels; DNA concentrations were measured with a NanoDrop 200 (Thermo Scientific) and adjusted to 25 ng ml 21 . We applied a slightly modified AFLP method described by Vos [40] (see the electronic supplementary material, notes and [25,24] for details).…”

“…The species flock is endemic to Lake Matano [20] and consists of several ecological specialists with conspicuous morphological and behavioural adaptations to various ecological niches [21][22][23]. However, specific morphotypes do not form well-sorted clades in phylogenetic analyses based on mitochondrial markers [24].…”

Dynamic switching in predator attack and maternal defence of prey

“…Oophagus species are found across many taxa (e.g. Coelho, Malaquias & Calado, 2006;de Queiroz & Rodriguez-Robles, 2006;Koedam, Aponte & Imperatriz-Fonseca, 2007;Cerwenka et al, 2012). Oophagy can be obligatory, depending entirely on eggs (Kam, Chuang & Yen, 1996;Li, Fry & Kini, 2005), or opportunistic, depending on nutritional needs or availability of eggs (Ochi, Sato & Yanagisawa, 1999;Denoel & Demars, 2008).…”

Age estimates for an adaptive lake fish radiation, its mitochondrial introgression, and an unexpected sister group: Sailfin silversides of the Malili Lakes system in Sulawesi

“…About 30 morphospecies of these sexually dimorphic fishes that typically possess bright male colourations are distinguished in the Malili Lakes drainage and a few surrounding rivers [ 11 ]. Sailfin silversides show conspicuous colour polymorphisms [ 12 , 13 ], and there are clear indications that ecological speciation has shaped their adaptive radiation [ 14 - 16 ]. Phylogenetic analyses suggest that the two lineages of Telmatherina radiating in the hydrological head of the lakes system, ancient graben-lake Matano, form an ancient monophyletic group that was later compromised by introgressive hybridization from stream populations [ 17 ].…”