Benefits of Dispersal in Patchy Environments: Mate Location by Males of a Wing-Dimorphic Insect Gail A. Langellotto; Robert F. Denno Ecology, Vol. 82, No. 7. (Jul., 2001), pp. 1870-1878. Stable URL: http://links.jstor.org/sici?sici=0012-9658%28200107%2982%3A7%3C1870%3ABODIPE%3E2.0.CO%3B2-1 Ecology is currently published by The Ecological Society of America. Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/esa.html. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is an independent not-for-profit organization dedicated to and preserving a digital archive of scholarly journals. For more information regarding JSTOR, please contact [email protected]. http://www.jstor.org Wed Apr 25 10:28:23 2007 Ecology, 82(7), 2001, pp. 1870-1878 0 2001 by the Ecological Society of America BENEFITS OF DISPERSAL IN PATCHY ENVIRONMENTS: MATE LOCATION BY MALES OF A WING-DIMORPHIC INSECT GAILA. LANGELLOTTOAND ROBERTF. DENNO Depar-tment of Entomology, Unzversi~of Ma~ylanrl.College Park, Ma~ylancl20742 USA Abstract. Dispersal dimorphisms, in which both flight-capable and flightless adults occur in the same species, are commonplace in insects. Such dimorphisms are seen as reflecting a balance between the benefits and costs of flight and wing reduction or loss. In heterogeneous habitats, theory predicts that fitness trade-offs can favor the evolution of a dispersal dimorphism in which both flight-capable and flightless morphs are retained in the same population. Despite the wealth of theory, howevel; there has never been an explicit field assessment of how habitat heterogeneity directly influences the reproductive success of the flight-capable and flightless wing forms of an insect species. The objective of this research was to investigate how variation in habitat heterogeneity (vegetation structure) and female density influence mate location and thus the potential for reproductive success by the male wing forms of a salt marsh inhabiting insect, the planthop- per Prokelisia dolus. By placing unmated females in the field at different densities and in sparse and contiguous vegetation, we were able to compare the ability of male wing forms to locate stationary mates. Our data show that both vegetation structure and female density differentially influenced the ability of the male wing forms to locate mates. Flight-capable males located females and acquired matings far more frequently in sparse vegetation, whereas flightless males discovered females more often in contiguous vegetation. Flight-capable males located fe- males more effectively at low female densities, whereas flightless males discovered females more efficiently at higher female densities. Thus, natural variation in vegetation structure and female density are two important factors which combine to influence the mating success of each male wing form. We conclude that habitat heterogeneity in concert with the known reproductive penalties imposed by flight capability (reduced siring ability) interact to favor the persistence of the dispersal polymorphism in males of this planthopper species. Key words: clispersal; ,flightlessness; rnate location; plcrntizopper; Prokelisia dolus; trade-off between jight capability ancl reproclzccrion; wing polymorphism. INTRODUCTION risk of mortality associated with the flight process itself Dispersal by flight is considered essential for the @off 1984, 1990, Zera 1984, Denno et al. 1989, Denno success of insects exploiting transient habitats (South- and 1990, Roff and 1991, Wagner wood 1977, Harrison 1980, Roff 1990, Denno et al, and Liebherr 1992). Such energetic costs are frequently 1991, 1996, Roff and Fairbairn 199 Zera and Denno imposed on reproduction, and are most easily assessed 1997). a is also to facil- in wing-dimorphic insects which occur as both flight- itate the search for mates, scattered food resources, and and (Roff 1984, Denno et ". 1989, 1991). In females of wing-dimorphic crickets, optimal oviposition sites ( D et al,~ 19g1,~ ~ ~and f ~ f Fairbairn 1991, Wagner and Liebherr 1992, Denno seed bugs, and planthoppers, for flight- 1994,~).In theory, dispersal can have a strong stabi. wing form often exhibits reduced lizing influence on local population fluctuations, and it extended age to first re~roduction,or reduced offspring is viewed as a central process in metapopulation dy- size compared to the flightless morph (Roff 1986, Sol- namics (den B~~~ 1981, ~~~l~~1990, ~~~~~~~i~~1995, heck 1986, Denno et al. 1989, Roff and Fairbairn 1991, Denno and Peterson 1995, Hanski and Kuussaari 1995). and 1997). *lthough it has proved M ~ dispersal~ also directly~ influences~ ~ gene flow~ difficult~ to demonstrate,, a growing body of literature and the genetic structure of populations (Pashley et al. Suggeststhat too pay the price abil- 1985, Preziosi and Fairbairn 1992, Peterson and Denno ity (Zera and Denno 1997, Langellotto et al. 2000). For 1997, 1998). instance, flight-capable males of a variety of insect taxa ~ i ~however,~ ~does ~not occur~ ~ withoutl costs,, are less aggressive in male-male interactions (Ichikawa costs such as the inherent expense of wings and flight 1982), (NovOtn~1995), repr0- muscles as well as the direct energetic penalties and ductively mature later in life (Utida 1972, Fujisaki 1992), attract fewer females and acquire fewer matings Manuscript received 23 June 2000; accepted 6 July 2000; final (Cres~i1988, Kaitala and Dingle 1993, Crnokrak and version received 1 August 2000. Roff 1995, 2000, Novotny 1995, Langellotto et al. 1870 July 2001 MATE LOCATION BY MALE PLANTHOPPERS 1871 2000), or sire fewer offspring (Langellotto et al. 2000) is probably essential for males to move among plants than their flightless counterparts. Thus, there is wide- in search of calling females (see Ichikawa and Ishii spread evidence for a trade-off such that dispersal abil- 1974, Hunt and Nault 1991). Third, confined on a single ity constrains reproduction and vice versa (Roff and host plant in a rival-male setting, flightless males own Fairbairn 1991, Zera and Denno 1997). a mating advantage over macropterous males because When the demands for flight relax, reduced dispersal they acquire most of the matings (Langellotto et al. capability or the loss of wings altogether can result 2000). Moreover, a trade-off between reproduction and (Roff 1990, Denno et al. 1991, 1996, Denno 1994~). dispersal capability has been demonstrated for male Most frequently, flightlessness or reduced dispersal planthoppers (Novotny 1995, Langellotto et al. 2000). ability is observed in insects which occupy persistent In P. dolus, brachypterous males sire twice as many habitats (Roff 1990, Denno et al. 1991, 1996, Denno offspring as macropterous males when females are 1994b, Zera and Denno 1997). In heterogeneous hab- abundant (Langellotto et al. 2000). What remains un- itats, however, theory predicts that fitness trade-offs known is how habitat heterogeneity and female density may favor the evolution of a dispersal dimorphism in might directly influence the mating success of the male which both flight-capable and flightless morphs occur wing forms, and in particular what environmental pa- in the same population (Harrison 1980, Roff 1984, rameters might favor flight-capable males in acquiring 1986, 1996, Denno et al. 1991, Roff and Fairbairn mates. Specifically, we hypothesize that flight-capable 1991, Denno 1994b, Ott 1994). Such dimorphisms are males will locate mates more effectively than flightless commonplace in the insects (Harrison 1980, Zera 1984, males in noncontiguous vegetation and when females Roff 1986, Denno et al. 1989, Roff and Fairbairn 1991, are rare. By comparing the ability of the male wing Zera and Denno 1997), and are seen as reflecting a forms to locate females under variable conditions, we balance between the costs and benefits of flight capa- seek to elucidate the benefits of dispersal in patchy bility and wing reduction (Fairbairn 1988, Denno et al. habitats. Such information is essential for understand- 1991, Roff 1996). Moreover, the observed frequency ing the selective forces associated with habitat hetero- of the flight-capable morph in the population is thought geneity that favor the persistence of flight polymor- to reflect the strength of selection for dispersal (Roff phism~. 1984, 1986, Fairbairn 1988, Denno et al. 1991, 1996). NATURALHISTORYOF STUDYORGANISMS Although the reproductive penalties associated with Planthopper population biology and plant flight are well documented in wing-dimorphic insects, heterogeneity there has never been an explicit field assessment of the benefits of dispersal in the context of mate location in Prokelisia dolus is an abundant sap-feeding herbi- heterogeneous habitats. vore (densities up to 1000 adults/m2) on the intertidal The objective of this research was to investigate how marshes along the Atlantic and Gulf Coasts of the Unit- variation in habitat heterogeneity (vegetation structure) ed States, where it feeds in the phloem of the perennial and female density influence mate location and thus grass, Spartinn alternijora (Denno et al. 1996). Al- though population densities of this multivoltine plant- the potential for reproductive success by the male wing hopper can be high, they also fluctuate dramatically forms of the salt marsh-inhabiting planthopper, Pro- kelisia dolus (Hemiptera: Delphacidae). We selected (Denno and Roderick 1992, Denno et al. 1996). P. dolus occurs primarily in meadow and panne (mud the male sex to study, because only males actively dis- flat) habitats on the high Spnrtina marsh (Denno et al. perse in search of mates in planthoppers (Claridge 1996).