Web image search revealed large‐scale variations in breeding season and nuptial coloration in a mutually ornamented fish, Tribolodon hakonensis

Abstract

Geographic variations in reproductive traits are important for evolutionary biology, but often difficult to investigate because of the need for a large‐scale survey and the ephemeral nature of secondary sexual characteristics. Here, using web image searches (Google Images and Twitter), we revealed large‐scale geographic variations (>1500 km) in breeding timing and nuptial coloration in the mutually ornamented fish, Japanese dace (Tribolodon hakonensis). As this fish is easily caught and many anglers upload their photographs on the web, we were able to find a total of 401 high‐resolution photographs from all over Japan. Breeding periods were determined from dates of photographs with/without nuptial coloration, which matched with previous studies. We also found that breeding periods might have advanced three weeks over the last 80 years in the Chitose River, potentially because of climate change. Additionally, the pattern of latitudinal cline for breeding timing revealed delayed timing in higher latitudes, although regional variations were also high. Finally, we quantified the patterns of nuptial coloration for this mutually ornamented fish, and confirmed that over 80% of individuals showed typical colorations, but others showed rare phenotypes that were never previously described, including an intermediate coloration between T. hakonensis and a potentially hybridizing species, T. brandtii. Our web‐based method for estimating breeding phenology could be adopted for organisms with temporal sexual characteristics, such as plants (e.g., flowering time) and some fishes. Web image analyses are still preliminarily with many limitations, but could be promising for investigating variations in visible traits.

Visual-based male mate preference for conspecific females in mutually ornamented fish: possible importance of species recognition hypothesis

“…Th shows greater variation in nuptial coloration patterns in regions where it is allopatric with its hybridizing species (i.e. Ts and T. brandtii) than in regions where it is sympatric with those species (Atsumi and Koizumi 2017b). If the nuptial coloration of Th contributes to sexual isolation as suggested by the present study, selection against hybridization should favor species-specific color patterns in sympatric regions, thereby reducing the variation in nuptial coloration of Th in those regions.…”

Native and introduced Far Eastern daces, genus Tribolodon, in the Tama River system, Japan, inferred from mitochondrial DNA analysis

“…1a). We compared the breeding color patterns of the T. hakonensis specimens in the present study (n = 191) with those described by Atsumi and Koizumi (2017), and found that the former matched those of populations in the Tama, Chikuma (Nagano), and Chitose (Hokkaido) Rivers [Fig. 2b, d in Atsumi and Koizumi (2017)].…”

“…The specimens were examined using two morphological keys, the cephalic lateral line system and breeding color, which have been used to identify T. hakonensis and T. brandtii previously (Sakai 1995;Sakai and Amano 2014;Atsumi and Koizumi 2017). T. brandtii maruta can be distinguished from T. hakonensis by the connection of the preoperculo-mandibular canal of the cephalic lateral line system to the postocular commissure (Sakai and Amano 2014); the presence or absence of this connection can be observed in fish larger than 80 mm SL (Kurawaka 1977).…”

Evaluation of Age-Dependent Changes in the Coloration of Male Killifish Nothobranchius Guentheri Using New Photoprocessing Methods

“…Brightly colored body areas (zones) predetermine sexual behavior and mate choice [ 43 ] and are primally located on the lateral side of fish. In other fish species, similar zones with similar functional significance can be distinguished [ 43 , 44 ].…”