Cuckoldry rates in the Molly Miller (Scartella cristata; Blenniidae), a hole-nesting marine fish with alternative reproductive tactics

Microsatellite markers were developed and employed to assess genetic maternity and paternity of embryos in nest-tended clutches of the Molly Miller (Scartella cristata), a marine fish in which alternative reproductive tactics (ARTs) by males were recently described from behavioral and morphological evidence. Genetic data gathered for 1,536 surveyed progeny, from 23 barnacle-nest holes in a single Floridian population, indicate that on average about 5.5 females (range 3–9) contributed to the pool of progeny within a nest. With regard to paternity, the microsatellite data demonstrate that most of the surveyed nests (82.6%) contained at least some embryos that had not been sired by the nesttending (bourgeois) male, and overall that 12.4% of offspring in the population had been sired via ‘‘stolen’’ fertilizations by other males. These are among the highest values of cuckoldry documented to date in nesttending fishes, and they support and quantify the notion that the nest-parasitic ART is reproductively quite successful in this species despite what would otherwise seem to be highly defensible nesting sites (the restricted interior space of a barnacle shell). Our estimated cuckoldry rates in this population of the Molly Miller are compared to those previously reported for local populations in other nest-tending fish species, with results discussed in the context of ecological and behavioral variables that may influence relative frequencies of nest parasitism. Introduction In fish species with external fertilization and extended parental care of offspring in nests (usually by males), intense competition for access to mates and fertilizations has frequently led to the evolution of male alternative reproductive tactics (ARTs) (Gross 1991, 1996; Taborsky 1994, 2001). Such ARTs, as behaviorally defined, are often associated with distinctive morphological features of the fish as well (Gross 1982; Gross and Charnov 1980; Gross and Shine 1981; Taborsky 1997). Probably the most common dichotomy is between bourgeois males (nest tenders) and parasitic sneakers (Taborsky 1998). Bourgeois males typically are large, display colorful secondary sexual characters, actively court females, and tend nests (e.g., fan eggs and defend against predators). Sneaker males can be much smaller and less colorful, show no proclivity to tend nests, and often have much higher testis size relative to body mass (apparently an adaptation for sperm competition associated with nest parasitism; Taborsky 1998). Whenever a parasitic male ‘‘steals’’ some fraction of fertilization events from a bourgeois male, e.g., by sneaking onto his nest and releasing sperm during a spawning episode, the nesttender then becomes a foster parent and is said to have been cuckolded. The Molly Miller (Scartella cristata; Perciformes; Blenniidae) is an abundant combtooth blenny of temperate and tropical regions (Robins 1986). Found near the shoreline in rocky areas, its range in the tropical western Atlantic extends from Florida, Bermuda, and the northern Gulf through the Caribbean Sea to Brazil (Gilbert 2002; Robins 1986). The Molly Miller is a holedwelling species with external fertilization. Large nesttending (bourgeois) males, whose elongate bodies reach up to 10 cm in length, are highly territorial and also provide extended care to the embryos in their respective nests, which are usually the hollow empty shells of barnacles (McEachran 1998). However, a recent comparative study of body sizes, accessory features of the Communicated by P. W. Sammarco, Chauvin M. Mackiewicz (&) Æ E. E. Dakin Æ J. C. Avise Department of Genetics, University of Georgia, Athens, GA 30602, USA E-mail: [email protected] Fax: +1-706-5830359 Present address: B. A. Porter Department of Biological Sciences, Duquesne University, Pittsburgh, PA 15282, USA Marine Biology (2005) 148: 213–221 DOI 10.1007/s00227-005-0010-9 reproductive tract involved in sperm production and handling, and testicular glands involved in pheromone synthesis, coupled with behavioral monitoring, documented the presence of two other distinctive male reproductive morphotypes in S. cristata (Neat et al. 2003): non-reproducing satellites (medium-sized individuals that remain site-attached to a hole), and sneakers (small vagrant males that appear morphologically and behaviorally specialized for releasing sperm in larger males’ nests). In other blennioid species, intrasexual polymorphisms of these sorts have usually (but see also Neat and Locatello 2002) been taken as good indicators for the presence of ARTs and nest parasitism (Goncalves et al. 2003a, b; Miranda et al. 2003; Neat 2001; Oliveira et al. 2000, 2001a, b, 2002). Although indirect evidence for nest parasitism by males can emerge from morphological assessments and behavioral monitoring, marker-based genetic analyses have made it possible to quantify actual rates and patterns of reproductive cuckoldry in nature. Microsatellite markers, in particular, have proved invaluable for detecting and quantifying reproductive behaviors in fishes, including alternative reproductive tactics and mating systems (Avise et al. 2002; DeWoody and Avise 2001; Jones and Avise 2001). Here we develop and employ a battery of microsatellite markers to examine genetic parentage (maternity as well as paternity) in a Floridian population of S. cristata. Of particular interest are male cuckoldry rates, which paradoxically might be hypothesized to be either exceptionally high (because of a high density of Molly Miller nests at the surveyed locale, and the presence of a sneaker ART in this species), or exceptionally low (if the barnacle-hole nests are as physically defensible by bourgeois males as they would appear to be at face value). The genetic findings on cuckoldry rates will be interpreted in the context of earlier behavioral and morphological observations for this species. They will also be compared to similar microsatellite-based reports for local populations in other nest-tending species, in order to address various ecological and behavioral factors that might influence relative frequencies of nest parasitism in fishes. Materials and methods Sample collections and microsatellite development On 12 October 2002, a collection of Molly Millers was made from a single rock surface (148·204 cm) that is part of a rock jetty facing the Gulf of Mexico in St. Andrews State Park, Panama Beach, Florida. By snorkeling, we collected bourgeois males from their barnacle-hole nests and preserved them in ethanol. Each of 38 nest-tenders was captured by placing a hollow plastic tube, closed at one end, over his nest, and inducing the male to swim into the tube by gentle tapping on the tube. Each male’s nest was then scraped off the rock surface by chisel and hammer, and the embryos lining its inner wall were preserved in a 20% DMSO/saturated NaCl solution. Care was taken to ensure that each bourgeois male was correctly associated with his nest. An additional 29 individuals (males, females, and juveniles) found swimming on the rock surface were collected for microsatellite development and to estimate population allele frequencies at the loci