Lavinia

Baumsteiger, Jason & Moyle, Peter B., 2019, A reappraisal of the California Roach / Hitch (Cypriniformes, Cyprinidae, Hesperoleucus / Lavinia) species complex, Zootaxa 4543 (2), pp. 221-240 : 223-224

Lavinia and Hesperoleucus

One conundrum within the Hitch–Roach species complex is uncertainty regarding whether species should be placed in one genus or two genera. While the complex was originally divided between Lavinia and Hesperoleucus , multiple examples of hybridization between the genera suggest they are more closely related than separate genera designations would normally indicate. For example, CA Roach are known to hybridize with Hitch in the Pajaro and Salinas rivers in Monterey Bay drainages ( Miller 1945), in Coyote, Alameda, and Walnut Creeks in the San Francisco Bay region ( Miller 1963; Leidy 1984, 2007, pers. comm.), and in Sacramento-San Joaquin drainages ( Avise et al. 1975; Jones 2001). Hybrids were fertile in the Pajaro River; Avise et al. (1975) found 8% of Hitch examined to be F 1 hybrids and 5% to be backcrossed. Since it is unusual for two genera to be interfertile and because other endemic species in California do not appear to exhibit this behavior ( Avise et al. 1975; Avise & Ayala 1976; Moyle & Massingill 1981; Moyle 2002), it has been proposed these two species belonged in a single genus.

Aguilar & Jones (2009) found the two genera are closely related mtDNA lineages that could be considered to be one genus. Schönhuth et al. (2012), however, noted that while their mtDNA analyses supported this close relationship, their limited nuclear DNA results did not. Our recent study ( Baumsteiger et al. 2017) found the strongest genomic signal coincided with splitting samples into two genera. We discovered, however, that samples from the Pit River (Northern Roach) were a confounding factor, having mixed historical ancestry with both genera. It was estimated in one analysis that approximately 80% of the Northern Roach genome clustered with Hitch whereas only 20% clustered with CA Roach. But all subsequent analyses found Northern Roach to be a distinct species, on par with currently identified species. Thus Northern Roach appears to be the result of an ancient hybrid speciation event ( Mallet 2007) between ancestral Hitch and CA Roach but it is currently genomically different enough to warrant species status.

It is our conclusion that despite hybridization between individuals in the different genera, the distinctiveness of each genus is still strongly maintained and prevalent throughout the genomes interrogated. If results were more admixed, the argument for a single genus would be more plausible. We recognize admixture between genera is uncommon but note that not all mutations lead to post-zygotic barriers ( Abbott et al. 2013). Additionally, hybridization has been proposed between Roach/Hitch and other members of the subfamily Leuciscinae including Speckled Dace ( Rhinichthys osculus ), Arroyo Chub ( Gila orcuttii ), and the now extinct Thicktail Chub ( Gila crassicauda ) ( Greenfield & Deckert 1973; Hopkirk 1973). Thus the frequency of hybridization suggests reproductive barriers are poorly developed in the endemic minnows of California. Secondly, although Northern Roach represent an ancient hybridization event and cluster primarily with individuals from the Lavinia genus (~80% but only in the admixture analysis), we cannot definitively say they are Lavinia . Northern Roach still strongly resemble CA Roach in appearance (see below), but this may simply be the result of natural selection for the CA Roach morphotype. Future phylogenetic analyses between all genera within the family may provide the solution but it remains, as yet, unavailable. Thus, without universal agreement between genomic analyses or improved criteria for taxonomically delineating hybrids, we default to the original genus assignment by Snyder (1913). Therefore, the species of Hesperoleucus are as described below.