Direct Familiarity Does Not Alter Mating Preference for Sisters in Male Pelvicachromis taeniatus (Cichlidae)

Close inbreeding has often been shown to be extremely harmful because of the fixation of deleterious recessive alleles in inbred offspring (Charlesworth & Charlesworth 1987). As a consequence, inbred offspring often show reduced fitness compared with outbred offspring (inbreeding depression, Charlesworth & Charlesworth 1987). The ability to identify relatives (kin recognition, Hepper 1991) offers individuals the opportunity to avoid them actively as mating partners (Pusey & Wolf 1996). In the animal kingdom, there are numerous examples that individuals avoid mating with close kin using kin recognition mechanisms (e.g. fishes: Frommen & Bakker 2006; Gerlach & Lysiak 2006; birds: Nakagawa & Waas 2004; humans: Wolf 2004; Lieberman et al. 2007). However, the specific mechanisms of kin recognition are still disputed and probably differ between and also within species, depending on social context (Tang-Martinez 2001; Mateo 2004; Frommen et al. 2007a). Kin recognition can base either on direct familiarity (Porter 1988), also mentioned as prior association (Mateo 2004), or on indirect familiarity (Porter 1988), which is caused by phenotype-matching (Holmes & Sherman 1982; Mateo 2004). In social species individuals who are familiar from birth are usually relatives (sibs or parents). Therefore, recognizing direct familiar individuals is usually a reliable kin recognition mechanism. In species, in which encounters with unfamiliar kin – for example with older or younger sibs of a different cohort – are possible, kin recognition mechanisms evolved which are not based on direct but on indirect familiarity (phenotype matching). During phenotype matching, phenotypic cues of an unknown individual are compared either with the own phenotype (self-reference) or with phenotypic cues of familiar individuals, e.g. of individuals the choosing individual grew up with, which are Correspondence Timo Thünken, Institute for Evolutionary Biology and Ecology, University of Bonn, An der Immenburg 1, D-53121 Bonn, Germany. E-mail: tthuenken@evolution. uni-bonn.de