Chapter 12 Evolutionary conservation biology Craig A. Stockwell and Sujan M. Henkanaththegedara 12.1 Introduction Much applied research has focused on endangered poe- ciliids (e.g., Poeciliopsis spp.) as well as common and inva- oeciliids are of particular interest to con- sive poeciliids (e.g., Gambusia spp., Poecilia reticulata). In servation biologists for a number of reasons. First, fact, many poeciliids have been used as model systems to Pthey have become excellent models for conservation examine questions central to the fi eld of conservation biol- biologists due to their small size and rapid generation time ogy. Here, we provide an overview of the poeciliids from (Quattro & Vrijenhoek 1989; Leberg 1990, 1993). Second, the perspective of conservation biology. First, we review the many poeciliid studies have provided important insights geographic distribution of poeciliid biodiversity as well as on the rate of evolutionary diversifi cation (e.g., Endler associated threats. We then consider the impact of nonnative 1980; Reznick et al. 1990; Reznick et al. 1997; see also poeciliids on native species and ecosystems. We conclude by Pires et al., chapter 3; Breden & Lindholm, chapter 22; summarizing the role of selected poeciliid species as models Grether & Kolluru, chapter 6; Johnson & Bagley, chap- for studies in the emerging fi eld of evolutionary conserva- ter 4; Schlupp & Riesch, chapter 5), the ultimate source of tion biology (as conceptualized by Ferrière et al. 2004). biodiversity. Third, poeciliids are vulnerable to the same anthropogenic factors driving the current extinction crisis (e.g., habitat loss, invasive species). Paradoxically, one of 12.2 Diversity, conservation, and threats the greatest threats to poeciliids is the spread of heterospe- cifi c poeciliids (Minckley & Deacon 1968; Meffe 1985b; Poeciliid conservation status has changed considerably dur- Minckley & Jensen 1985; Courtenay & Meffe 1989; Belk ing the last few decades (Jelks et al. 2008). Here, we pro- & Lydeard 1994). Thus, poeciliids have been extensively vide a brief overview of poeciliid biodiversity with special evaluated in the context of conservation biology (Johnson focus on the conservation status of these fi shes. We also & Hubbs 1989; Leberg 1990, 1993; Stockwell et al. 1996; review the primary threats faced by poeciliids. Stockwell & Weeks 1999). Johnson and Hubbs (1989) provided an overview of the 12.2.1 Poeciliid biodiversity and distribution conservation status of the poeciliids in the United States. Since that time, poeciliids have mirrored the decline of other The FishBase data base (Froese & Pauly 2009) and recent freshwater fi shes (see Jelks et al. 2008). Furthermore, our reviews (Parenti 1981; Parenti & Rauchenberger 1989; understanding of relationships among taxa has increased, Nelson et al. 2004; Hrbek et al. 2007; Eschmeyer & Fong allowing reevaluation of the systematics and distribution of 2008; Jelks et al. 2008; Scharpf 2008) recognize more poeciliid biodiversity (Rosen & Bailey 1963; Parenti 1981; than 250 species of poeciliids, belonging to 22–28 genera. Parenti & Rauchenberger 1989; Hrbek et al. 2007). The most species-rich genera are Gambusia (43 species), You are reading copyrighted material published by University of Chicago Press. Unauthorized posting, copying, or distributing of this work except as permitted under U.S. copyright law is illegal and injures the author and publisher. C. A. Stockwell and S. M. Henkanaththegedara 129 Poecilia (34 species), Xiphophorus (28 species), Poecili- Poeser et al. 2005; Lucinda et al. 2006). For example, a opsis (23 species), Phalloceros (22 species), and Limia recent expedition in South America added 21 new species (21 species) (table 12.1). The Poeciliidae family is widely to the genus Phalloceros, which previously contained only distributed, occurring as native species from the south- 1 described species (Lucinda 2008). The known biodiver- eastern United States to northeastern Argentina (Rosen & sity of poeciliids (subfamily Poeciliinae = family Poecili- Bailey 1963; Nelson 2006). This clade of fi shes originated idae in Rosen & Bailey 1963) thus has grown from 194 in South America and dispersed to Central America and species in the late 1980s (Rauchenberger 1989) to more North America (Hrbek et al. 2007). than 262 valid species by 2008 (Eschmeyer & Fong 2008). Our understanding of poeciliids in South America and This number is likely to grow as more areas are intensively parts of Central America has increased markedly in the last sampled (Lucinda 2008). few decades (Meyer & Etzel 2001; Poeser 2002; Meyer Our knowledge of poeciliid diversity is further compli- et al. 2004; Lucinda 2005b, 2008; Lucinda et al. 2005; cated by discrepancies among workers in the recognition of particular taxa. For instance, topminnows native to the Gila River and Yaqui River drainages were originally Table 12.1 Number of species and distribution of poeciliid genera described as two species, Poeciliopsis occidentalis and P. in the world sonoriensis but were synonymized by Minckley (1969) as P. o. occidentalis and P. o. sonoriensis, respectively. How- Genus Number of species Distribution ever, based on a series of studies including a variety of mo- Alfaro 2 CA, SA lecular markers, these two taxa are now considered dis- tinct species (Vrijenhoek et al. 1985; Quattro et al. 1996; Belonesox 1 NA, CA Minckley 1999; Hedrick et al. 2006). Brachyrhaphis 12 NA, CA Here, we follow Parenti (1981) in recognizing Poecili- Carlhubbsia 2 CA idae as livebearing fi shes excluding South American Flu- Cnesterodon 9 SA viphylax and Old World relatives. Biodiversity of poeci- Gambusia 43 NA, CA, SA liids should also consider the recognition of conservation Girardinus 7 CA units— evolutionarily signifi cant units (ESUs)—although Heterandria 10 NA, CA this concept has not been widely applied within Poeciliidae Heterophallus 2 NA, CA (but see box 12.1). Limia 21 CA, SA Micropoecilia 5 CA, SA 12.2.2 Poeciliid conservation status Neoheterandria 3 CA, SA The conservation status of poeciliid species is best known Pamphorichthys 6 SA for populations in the United States; thus, knowledge of Phallichthys 4 CA the threats faced by poeciliids is based largely on studies Phalloceros 22 SA conducted for more northern species. For instance, the Phalloptychus 2 SA International Union for Conservation of Nature (IUCN Phallotorynus 6 SA 2008) evaluated the conservation status for a good portion Poecilia 34 NA, CA, SA of North American (including Mexico) poeciliids (22 spe- Poeciliopsis 23 NA, CA, SA cies) but for only 1 species in Central America and 1 species Priapella 5 NA, CA in South America (table 12.2). This is mainly due to poor Priapichthys 7 CA, SA understanding of the diversity, distribution, and natural history of Central American and South American poecili- Pseudopoecilia 3 SA ids (Lucinda et al. 2005; Lucinda 2008). Furthermore, the Quintana 1 CA Endangered Species Committee of the American Fisheries Scolichthys 2 CA Society (AFS-ESC) identifi ed 37 imperiled poeciliid taxa Tomeurus 1 SA from North America, including 32 (33% of total poecili- Xenodexia 1 CA ids) described species and 5 undescribed taxa/subspecies or Xenophallus 1 CA populations (Jelks et al. 2008; fi g. 12.1). Xiphophorus 28 NA, CA Unfortunately, the conservation status of poeciliids in North America has deteriorated in the last two decades, Source: FishBase (Froese & Pauly 2009) . with the list of imperiled taxa growing from 21 to 37 (Wil- Note: NA = North America; CA = Central America, and SA =South America. liams et al. 1989; Jelks et al. 2008). Furthermore, the con- You are reading copyrighted material published by University of Chicago Press. Unauthorized posting, copying, or distributing of this work except as permitted under U.S. copyright law is illegal and injures the author and publisher. 130 Chapter 12 Box 12.1 Conservation units and the management of P. occidentalis exhibit no mtDNA variation (sequence of desert topminnows data for 2626 bp) and therefore do not meet the crite- rion of reciprocal monophyly. Hedrick et al. (2006) ar- The Gila topminnow (Poeciliopsis occidentalis) provides gued that the requirement of reciprocal monophyly for an excellent opportunity to consider genetic manage- ESU designation was too restrictive. In fact, the absence ment of protected species. This species was once wide- of mtDNA variation was consistent with the theoretical spread but is now restricted to a small number of rem- expectations based on the period of known divergence nant populations (Minckley 1999). Because gene fl ow (10,000 years) (Hedrick et al. 2006). must be accomplished by translocation of fi sh, delinea- Based on the ESU criteria set forth by Crandall et al. tion of evolutionarily signifi cant units (ESUs) is of par- (2000), the two conservation units can be scored as eco- ticular interest to managers. logically and genetically nonexchangeable. Thus, a con- Moritz (1994) proposed the operational yet restrictive sensus seems to have emerged to recognize two ESUs of criterion that ESUs be defi ned as taxonomic units that P. occidentalis (box-fi g. 12.1) (Minckley 1999; Parker are reciprocally monophyletic at mitochondrial DNA et al. 1999; Hedrick et al. 2006). (mtDNA) markers. Crandall et al. (2000) suggested that conservation units be considered along a gradient based on genetic and ecological exchangeability. Units that are nonexchangeable are thus unreplaceable, making them evolutionarily signifi cant. Fortunately, Poeciliopsis species have been well