Heterospecific aggression bias towards a rarer colour morph

Abstract

Colour polymorphisms are a striking example of phenotypic diversity, yet the sources of selection that allow different morphs to persist within populations remain poorly understood. In particular, despite the importance of aggression in mediating social dominance, few studies have considered how heterospecific aggression might contribute to the maintenance or divergence of different colour morphs. To redress this gap, we carried out a field-based study in a Nicaraguan crater lake to investigate patterns of heterospecific aggression directed by the cichlid fish, Hypsophrys nicaraguensis, towards colour polymorphic cichlids in the genus Amphilophus. We found that H. nicaraguensis was the most frequent territorial neighbour of the colour polymorphic A. sagittae. Furthermore, when manipulating territorial intrusions using models, H. nicaraguensis were more aggressive towards the gold than dark colour morph of the sympatric Amphilophus species, including A. sagittae. Such a pattern of heterospecific aggression should be costly to the gold colour morph, potentially accounting for its lower than expected frequency and, more generally, highlighting the importance of considering heterospecific aggression in the context of morph frequencies and coexistence in the wild.

Allopatry, competitor recognition and heterospecific aggression in crater lake cichlids

“…In other words, contrary to our expectation, neither of the two focal species adjusted their aggression to the allopatric heterospecific signal. Earlier studies using both manipulated [ 19 ] and natural [ 22 ] stimuli have nevertheless strongly indicated that Amphilophus cichlids do react differently to sympatric breeders and non-breeders, with coloration (of model intruders) being a sufficient cue for aggression level adjustments in both of our focal species [ 18 , 19 , 38 ]. Below we discuss why we did not find adjustment of aggression towards the different models of A. astorquii intruders in the current study.…”

“…However, it is important to point out that earlier studies have demonstrated significant aggression adjustments to colour differences in similar intruder models (i.e. with a thickness of 6 mm) of sympatric species [ 18 , 19 , 38 ].…”

“…Specifically, we glued a waterproof, photographic colour print of the lateral side of a live or freshly euthanized specimen (sex unknown or not noted) onto each lateral side of an elliptical floating plate with a thickness of 6 mm. All our models were l6 cm long and attached to a sinker with a thin, transparent fishing line, so that they floated in a natural position approximately 15 cm above the lake bottom during the trials ([ 18 , 19 , 38 ]; Fig. 1 ).…”

Color and behavior differently predict competitive outcomes for divergent stickleback color morphs

“…Many of the study systems in which the role of male competition in speciation has been addressed are systems in which alternate color morphs are maintained within species (e.g. Kissenda Island cichlids ( Dijkstra et al 2005 ; Dijkstra et al 2009 ), sticklebacks ( Tinghitella et al 2015 ; Bolnick et al 2016 ), European wall-lizards ( While et al 2015 ), or in which color is a primary phenotype that differs between closely related species [e.g., lake Victoria cichlids ( Seehausen and Schluter 2004 ); Nicaraguan cichlids ( Lehtonen et al 2015) ; darters ( Martin and Mendelson 2016 ; Roberts and Mendelson 2017 ); rubyspot damselflies ( Anderson and Grether 2010 a, 2010 b), limnetic-benthic stickleback species pairs ( Lackey and Boughman 2013 ; Keagy et al 2016 )]. In a handful of these systems, variation in the sensory environment is implicated in color shifts ( Reimchen 1989 ; Boughman 2001 ; Scott 2001 ; Maan et al 2006 ; Seehausen et al 2008 ).…”

“…In simulated mixed color assemblages in the lab, black males from Washington state (WA) rivers biased their aggression toward males with red nuptial coloration, whereas red males show no bias in aggressive behavior ( Tinghitella et al 2015 ). This pattern of aggression (bias toward heterotypic males) suggests that red males are the recipients of more aggression overall which could allow black males to exclude red males from preferred breeding sites (e.g., Adams 2004 ; Peiman and Robinson 2007 ; Vallin and Qvarnström 2011 ; Winkelmann et al 2014 ; Lehtonen et al 2015) , enhancing habitat use differences. However, our understanding of how male competition might contribute to genetic divergence (through male competition outcomes) in this system has been limited by not knowing whether black nuptial coloration itself is related to male competition outcomes.…”