This article summarizes an experiment that tested female preferences in Xiphophorus variatus fish. The experiment had 3 parts that tested preferences for: 1) body size while holding dorsal fin size constant, 2) dorsal fin size while holding body size constant, and 3) dorsal fin to body size ratio while holding total lateral projection area constant. In all parts, researchers used dummy fish that varied one trait while holding others constant. Females spent more time near dummies with larger bodies and dorsal fins. However, females showed no preference based on dorsal fin to body size ratio when total area was held constant. This provides additional support that female preference in this species is for increased total lateral projection area rather than a specific trait or

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Behavioural Processes 87 (2011) 197–202
Contents lists available at ScienceDirect
Behavioural Processes
journal homepage: www.elsevier.com/locate/behavproc
Female bias for enlarged male body and dorsal fins in Xiphophorus variatus
R. David MacLaren a,∗ , John Gagnon b , Ran He c
a
Merrimack College, Department of Biology, Mendel Center, North Andover, MA 01845, USA
b
Immune Disease Institute, 100 Longwood Ave., Boston, MA 02115, USA
c
University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA
a r t i c l e i n f o a b s t r a c t
Article history: Female preference for male fin elaborations in Poeciliid fishes may be driven by a sensory bias for
Received 3 November 2010 increased lateral projection area (LPA) that has existed since the lineages diverged from a common
Received in revised form 22 March 2011 ancestor. Previous research supports this hypothesis demonstrating female Poecilia latipinna, Poecilia
Accepted 23 March 2011
mexicana, and Poecilia reticulata prefer males of larger body and dorsal fin size, but exhibit no such
preferences when controlling for total LPA. In the current study, we further tested this hypothesis by
Keywords:
presenting female platys, Xiphophorus variatus, with pairs of dummy males differing in: (1) body size
Female preference
(holding dorsal fin size constant); (2) dorsal fin size (holding body size constant); and (3) dorsal fin: body
Poecilidae
Sensory bias
size ratio (holding total LPA constant). Females spent more time near dummies of greater body and dorsal
Sexual selection fin size; however, in the third experiment, neither fin size, body size, nor any particular dorsal fin + body
Xiphophorus variatus size combination was preferred. These results provide additional support for the LPA and sensory bias
hypotheses, demonstrating that female X. variatus not only prefer males with “swords”, but sailfin-like
dorsal fins as well when body size is held constant. Shared preference for increased LPA is consistent with
common ancestry of the sensory/neural systems in females of all four species.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction species find attractive (e.g. X. maculatus; Basolo, 1990b, Xiphophorus
variatus; Basolo, 1995b, Priapella olmecae; Basolo, 1995a). Phylo-
Females may develop perceptual biases in mate preferences due genetic information and mate choice tests suggest that female
to a sensory bias in their nervous systems formed by natural selec- preference for swords arose before the Xiphophorus-Priapella clade
tion, sexual selection, or pleiotropic effects (Kirkpatrick and Ryan, diverged, pre-dating the evolution of the sword within Xiphophorus
1991; Endler, 1992). Such biases may reflect ecological constraints (Basolo, 1996).
(Proctor, 1991; Endler, 1992) or basic properties of nervous sys- Species within the subgenus Poecilia (mollies) provide addi-
tems (Ryan and Keddy-Hector, 1992; Rosenthal and Evans, 1998; tional evidence of female bias for male fin elaborations. Male sailfin
MacLaren, 2006). Regardless of the bias origin, females are pref- mollies (Poecilia latipinna) have an enlarged dorsal fin (sailfin) that
erentially attracted to males that stimulate their sensory systems is presented to females in courtship (Ptacek and Travis, 1996).
more than other males. If a male sends a novel signal which taps Female P. latipinna as well as Poecilia mexicana (a species whose
into a latent bias, these males are preferred as mates. Thus, a pre- males do not naturally possess the sailfin phenotype) prefer to
existing bias may affect the nature and direction of sexual selection associate and mate with males of larger dorsal fin (MacLaren et al.,
when a new trait arises (Basolo, 1995a). 2004; MacLaren and Rowland, 2006; Jordan et al., 2006) and body
Support for the preexisting bias hypothesis requires evidence size (Ptacek and Travis, 1997; MacLaren et al., 2004; MacLaren
that the female preference evolved within the species’ lineage and Rowland, 2006). As with the sword ornament of Xiphopho-
prior to the evolution of the male trait that exploits the preference rus, phylogenetic information (Ptacek and Breden, 1998; Breden et
(Basolo, 1990a). The role of preexisting biases on female preference al., 1999) suggests that female preference for enlarged dorsal fins
for male traits has been well studied in certain species of live- arose before the monophyletic sailfin clade diverged from a short-
bearing fishes (Poecilidae). For example, males of some species of fin ancestor, pre-dating the evolution of the sailfin trait within the
the genus Xiphophorus possess an elongation of certain ventral cau- subgenus Poecilia.
dal fin rays (the sword) that even females of related but unsworded Additionally, males of numerous guppy populations (Poecilia
reticulata) show polymorphism in dorsal and caudal fin length
including homoplastic “swords”, elongated tails and enlarged
∗ Corresponding author. Tel.: +1 9788373543. dorsal fins (Houde, 1997; Brooks and Endler, 2001; Karino and
E-mail address: maclarenr@merrimack.edu (R.D. MacLaren). Matsunaga, 2002; MacLaren et al., submitted for publication)
0376-6357/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.beproc.2011.03.006

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198 R.D. MacLaren et al. / Behavioural Processes 87 (2011) 197–202
that along with body size (Endler and Houde, 1995; Karino and preference (expt I), dorsal fin preference (expt II), and fin: body size
Matsunaga, 2002; MacLaren et al., unpublished data) offer a selec- ratio preference (expt III). All three experiments were run concur-
tive advantage in female mate choice in at least some populations rently between December 2008 and May 2010 as time permitted.
(Bischoff et al., 1985; Endler and Houde, 1995; MacLaren et al., All fish were kept in the laboratory under similar conditions for the
submitted for publication). same amount of time throughout the testing period.
These elongated caudal and dorsal fins, among other poeciliid
fin elaborations may have originated from a shared female prefer- 2.2. Dummy construction
ence for larger apparent size in males, a preference that is common
in many species (Andersson, 1994) and widespread among the Poe- In order to control for variation in male behavior among other
cilidae (Ryan, 1998). Because a larger male projects a larger image traits, we used dummy males as stimuli, varying one trait (body
onto the female’s retina at a given viewing distance (O’Brien et al., size in expt I, dorsal fin size in expt II, and dorsal fin: body size
1976, 1985; Rowland, 1989a,b), this could elicit a stronger sexual ratio in expt III) while holding all other traits constant. The use of
response (MacLaren, 2006). Fin elaborations may therefore have dummies allowed us to modify each variable independently while
evolved as a way for males to increase their apparent size or lat- compromising little in the way of visual detail (Rowland, 1999). The
eral projection area (LPA) and consequent attractiveness to females dummies were produced as described in MacLaren et al. (2004). The
(Haines and Gould, 1994; Rosenthal and Evans, 1998; Karino and Constant Fin Size Series for expt I consisted of three images mea-
Matsunaga, 2002; MacLaren et al., 2004). suring 35, 45 and 55 mm from the anterior tip of the fish to the end
If females respond primarily to greater LPA rather than increased of the caudal fin, with proportional increases in the sizes of all fins
body or fin size per se, then female preference should be propor- except the dorsal, which was held constant at 12.5 mm in length
tional to the male’s total LPA (body + fin area) regardless of his fin: (approximating the average dorsal fin size of mature males in our
body size ratio (MacLaren et al., 2004). The LPA hypothesis predicts laboratory population, unpublished data). The Constant Body Size
that females: (1) prefer males of larger body and fin size; (2) show Series for expt II consisted of three images all measuring 45 mm
no preference between two males whose total LPAs (fin + body sur- from the anterior tip of the fish to the end of the caudal fin (approx-
face areas) are equal (i.e. increases in fin surface area compensate imating the average total length of mature males in our laboratory
for decreases in body surface area and vice versa); and (3) show no population, unpublished data) with dorsal fins measuring 12.5, 17.5
preference for males with the fin elaboration over a finless male of and 22.5 mm in length and proportional changes in fin allometry
equivalent LPA. Preference experiments with P. latipinna (MacLaren (i.e. no changes in fin shape). The Constant Body Ratio Series for
et al., 2004), P. mexicana (MacLaren and Rowland, 2006), and P. retic- expt III consisted of five dummies that differed in dorsal fin: body
ulata (MacLaren et al., submitted for publication) support all three size ratio. The dummies included a male with no dorsal fin, and
of the predictions above. males with 0.28, 0.55, 0.83, and 1.11 cm2 fins with compensatory
In this study we further test the LPA hypotheses by examining decreases in body area to ensure that all five maintained a constant
female preferences for male body size, dorsal fin size, and dorsal LPA of 5.06 cm2 . This constant was determined by calculating the
fin: body size ratio in X. variatus—a series of experiments similar composite LPA of a male of average dorsal fin and body size from our
to those previously conducted with P. latipinna, P. mexicana, and study population (unpublished data). Thus, the dummies for expt III
P. reticulata. Moreover, we want to know whether this preference were designed such that the difference in body LPA between males
stems from a preexisting bias. Female preference for increased male in all 10 paired combinations of the five stimuli were equal to their
LPA not only in the subgenera Poecilia (“mollies”) and Lebistes (“gup- difference in dorsal fin LPA.
pies”) but the more distantly related genus Xiphophorus would The dummies were identified as ‘small’ (S), ‘intermediate’ (I)
support the preexisting bias hypothesis, demonstrating that female and ‘large’ (L) in experiments I and II, in correspondence with their
X. variatus (a species sexually monomorphic with respect to fin dorsal fin size/total lengths. For the fin: body ratio series (expt III),
morphology) not only prefer males with artificial “sword” orna- each dummy within a series was assigned a ranking from “1” to “5”
ments (Basolo, 1995b) but supernormal size dorsal fins and perhaps in relation to its body LPA, from smallest (1) to largest (5) (Fig. 1).
other forms of size manipulation that increase male LPA (Haines
and Gould, 1994). A shared preference for sailfin-like dorsal fins 2.3. Testing apparatus and procedure
and/or increased LPA would be consistent with common ancestry
of the sensory/neural systems in females of P. latipinna, P. mexicana, The testing environment consisted of three 17.5-l aquaria
P. reticulata, and X. variatus. (50 cm × 26 cm × 13.5 cm each) lined up end to end using an
apparatus and protocol identical to that used in previous mate
2. Methods preference experiments with Xiphophorus helleri (MacLaren and
Daniska, 2008) and P. reticulata (MacLaren et al., submitted for
2.1. Subjects publication). Female subjects were placed in an aquarium that
was divided into three zones by two black vertical lines drawn
Test subjects were X. variatus, Zarco collected from the Arroyo on the front wall: a 30 cm × 26 cm × 13.5 cm ‘neutral zone’ flanked
Zarco locality west of Encino, Tamaulipas, Mexico (locale described on each side by a 10 cm × 26 cm × 13.5 cm ‘preference zone’. A pair
by Borowsky (1984); stock source: Dr. Steve Kazianis, New York of aquaria flanking the female’s tank each housed an adjustable
University, 6th of September 1996). The fish were shipped to the motorized belt and pulley system to which the dummy stimuli were
laboratory at Merrimack College from the Xiphophorus Genetic attached (see MacLaren and Daniska, 2008 for further details).
Stock Center, Texas State University, San Marcos, TX in the fall Each subject (expt I: n = 23; expt II: n = 22; and expt III: n = 22)
of 2008, placed in 378-l and 70-l mixed-sex stock tanks (water was introduced into the center aquarium and allowed to acclimate
temperature 23–25 ◦ C; 16 h light:8 h dark cycle) and fed TetraMin for 15 min. Opaque screens blocking the female’s view of the dum-
fish flakes two times daily. We removed females from stock tanks mies were then removed and the apparatus was turned on so that
at random and placed them in 70-l all-female subject tanks for a the dummies began to move. Using a Canon ZR930 digital video
minimum of two months prior to testing. Females were then trans- recorder, the female’s behavior was recorded for 5 min. The dum-
ferred to separate 8.75-l isolation tanks (30 cm × 15 cm × 20 cm) for mies were then switched to opposite sides of the arena for another
approximately 48 h before becoming eligible for use as subjects. 5 min of observation for a total of 10 min of testing per treatment.
Each female was subjected to one of three experiments: body size The subject was left undisturbed for 5 min before proceeding to the

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R.D. MacLaren et al. / Behavioural Processes 87 (2011) 197–202 199
Fig. 1. Dummy males varying in body size, dorsal fin size, and dorsal fin-to-body size ratio used in expts. I, II, and III, respectively. Dummy letter designations S, I, and L
(top left margin) correspond to the small, intermediate, and large body and fin size variants for experiments I and II. Dummy number designations 1–5 (bottom left margin)
correspond to dorsal fin: body size variants from smallest (1) to largest (5) body size used in expt III.
next treatment of the series. For experiments I and II, all three pos- 3. Results
sible paired combinations of the three dummies (dummy ‘L’ paired
with dummy ‘S’, ‘L’ with ‘I’, and ‘S’ with ‘I’) were presented in ran- The female behaviors observed during both experiments
dom order to each female in a single day. In expt. III, all 10 paired included unison swimming, circling, and backing toward the male,
combinations of the five dummies were presented in random order all of which are activities attributed to mating behavior in the liter-
to each female over a period of two days; five of the 10 paired com- ature for poeciliids (Farr, 1989; Houde, 1997; Basolo, 2002a). There
binations on each day of testing (MacLaren and Daniska, 2008). No were no significant effects of dummy presentation order on female
female was subjected to more than one set of treatments (i.e. one strength of preference in any of the three experiments (expt I: one-
experiment). way repeated measures ANOVA, df = 2, F = 0.327, P = 0.723; expt II:
one-way repeated measures ANOVA, df = 2, F = 0.186, P = 0.831; expt
III: one-way repeated measures ANOVA; df = 9, F = 0.982, P = 0.456).
2.4. Behavioral measures and statistical analyses Additionally, female total length (±SE) did not differ across exper-
iments (expt I: 35.4 ± 0.05 mm, max = 4.10, min = 3.10; expt II:
As in previous experiments of this kind (MacLaren et al., 2004, 36.0 ± 0.06 mm, max = 4.10, min = 3.00; expt III: 36.3 ± 0.06 mm,
submitted for publication; MacLaren and Rowland, 2006; MacLaren max = 4.20, min = 3.10; df = 2, F = 0.659, P = 0.521). Moreover, we
and Daniska, 2008), we played back all video data in real time found no evidence of female size differentially affecting female
to determine the total time each female spent in each prefer- preference across treatments within any of the three experiments
ence zone as well as time spent in the neutral zone per 10-min given that: (1) all subjects received all treatments within an exper-
treatment. Paired samples t-tests were used to compare the total iment and (2) one-way repeated measures ANOVAs revealed no
time females spent in association with dummy A vs. dummy effect of female total length on strength of preference in any of the
B in each treatment (e.g. L vs. S treatment of expt I). Female three treatments of experiments I (n = 23) and II (n = 22), nor in any
strength of preference was defined as time spent with dummy of the ten treatments of expt III (n = 22).
A − time with dummy B per 10 min treatment. Because each female Paired samples t-tests comparing the total time females (n = 23)
received three treatments in experiments I and II, and ten treat- spent with the larger- vs. smaller-bodied male dummy and asso-
ments in expt III, all significance levels were adjusted to P < 0.017 ciated reports of the effect size (Cohen’s d with 95% confidence
and P < 0.005, respectively (Bonferroni procedure; Sokal and Rohlf, interval) in experiment I revealed that females spent significantly
1981). All probabilities given are two-tailed. In order to make eas- more time with the larger bodied of the paired males in each
ier inters-study comparisons, we used Cohen’s d to calculate the of the three treatments (P < 0.017; Table 1 and Fig. 2). Similarly,
effect size (with 95% confidence interval) related to the preference paired samples t-tests and associated Cohen’s d calculations com-
strength for each treatment in all three experiments (Nakagawa paring the total time females (n = 22) spent with the larger- vs.
and Cuthill, 2007). We conducted all statistical tests using the smaller-finned male in experiment II revealed a preference for the
statistical program Sigmastat Ver. 11.2 (Systat Software, Point Rich- larger-finned dummy in all three treatments (P < 0.017; Table 1 and
mond, CA, USA) with the exception of effect size calculations, which Fig. 2).
were made using software by David B. Wilson available online at However, paired samples t-tests comparing total time females
http://mason.gmu.edu/∼dwilsonb/ma.html. (n = 22) spent in association with the larger-bodied, smaller-finned

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200 R.D. MacLaren et al. / Behavioural Processes 87 (2011) 197–202
Fig. 2. Results from expt I, II, and III. (a) Expt I: The average amount of time (s) females (n = 23) spent in association with the smaller vs. larger of two dummy males in each of
three 10 min treatments (dummy I vs. S, L vs. S, and L vs. I). (b) Expt II: The average amount of time (s) females (n = 22) spent in association with the smaller vs. larger of two
dummy males in each of three 10 min treatments. (c) Expt III: The average amount of time (s) females (n = 22) spent in association with the smaller-bodied, larger-finned vs.
larger-bodied, smaller-finned of two dummy males in each of ten 10 min treatments. * indicates Bonferroni corrected significant preference (paired samples t-tests; P < 0.017)
for the larger of the paired males.
male vs. the smaller-bodied, larger-finned male in experiment III 4. Discussion
revealed no significant preferences in any of the 10 treatments
(P > 0.005; Table 2 and Fig. 2). Thus, females did not exhibit a pref- As demonstrated in similar studies with P. latipinna, P. mexicana,
erence for any particular male across treatments in experiment III, and P. reticulata, the preferences of female X. variatus satisfy all
including the dummy that best approximated the fin: body ratio three predictions of the LPA hypothesis, suggesting that increased
of a typical X. variatus male (dummy no. 3; Fig. 1). Furthermore, dorsal fin size can compensate for decreased body size and vice
in none of the four treatments that involved dummy no. 5 (a male versa, and that preference is for male LPA rather than for dorsal fin
lacking a dorsal fin; Fig. 1) did females prefer to associate with the and body size per se. Haines and Gould (1994) explored the basis
alternative dummy that possessed a dorsal fin. of female preference for a male fin elaboration – the sword – in X.

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R.D. MacLaren et al. / Behavioural Processes 87 (2011) 197–202 201
Table 1 benefits correlated with male size (reviewed in MacLaren et al.,
Results from experiments I and II (female preference for male body and dorsal fin
2004; MacLaren and Rowland, 2006). Alternatively, such a prefer-
size, respectively): mean female strength of preference (SOP) (i.e. time spent in
association with the larger male–time with the smaller male per 10 min test period) ence may be a correlated response to selection on male choice of
in each of three treatments of expt I (n = 23) and expt II (n = 22). Results of paired larger, more fecund females (Ptacek and Travis, 1997; Gabor, 1999;
samples t-tests comparing total time (s) females spent in association with the larger Herdman et al., 2004; Dosen and Montgomerie, 2004).
vs. smaller male in each treatment and associated Cohen’s d calculations of the effect From the males’ prospective, if greater LPA increases attractive-
size (with 95% confidence interval) related to preference strength (Nakagawa and
Cuthill, 2007).
ness to females and improves reproductive success, then selection
should favor male allocation of energy to body parts such as dor-
Treatment Mean SOP (s) t-value p-value Cohen’s d (95% C.I.) sal and caudal growth that maximize total LPA. This, however,
Experiment I: preference for male body size (fin size control series) assumes that females have opportunities to choose amongst males
I vs. S 114.4 ± 35.7 3.20 0.004 1.147 (0.523–1.771) and that the costs of trait expression (e.g. increased predation
L vs. S 116.9 ± 28.1 4.16 < 0.001 1.253 (0.621–1.885)
or decreased swimming performance) do not exceed the mat-
L vs. I 109.2 ± 36.9 2.96 0.007 0.923 (0.319–1.54)
Experiment II: Preference for male dorsal fin size (body size control series) ing benefits. Violation of either or both assumptions, along with
I vs. S 104.4 ± 36.0 2.90 0.009 0.958 (0.334–1.582) genetic/developmental constraints, may explain the traits’ absence
L vs. S 134.0 ± 29.7 4.51 <0.001 1.512 (0.842–2.182) in male X. variatus.
L vs. I 97.3 ± 36.6 2.65 0.015 0.9561 (0.3323–1.58) There is morphological and ontogenetic evidence that the
swords and sailfin-like fins found in Xiphophorus, sailfins in mol-
lies, and sword- and sailfin-like fins observed in certain populations
variatus and came to a similar conclusion, suggesting that the gen-
of P. reticulata, have separate evolutionary origins (Rauchenberger
eral feature females are responding to is total length as measured
et al., 1990; Basolo, 1996; Breden et al., 1999) and thus resemble
along the male’s ventral surface rather than sword or tail length per
one another as a result of parallel evolution (Basolo, 1995a). The
se. Females in the current study, however, did not base their pref-
common selective force behind such convergence may be female
erences on total length alone. If they had, we would expect females
bias for males of larger apparent size or LPA. Just as the same initial
to prefer the larger-bodied, smaller-finned dummies in experiment
bias may select different traits in different lineages (e.g. a sword
III, which did not occur. Still, the results of both studies suggest that
vs. a sailfin) depending on the chance appearance of new variation,
female preference in platys may be for males of larger apparent size
an initial bias could select for similar traits in different lineages
(Rosenthal and Evans, 1998).
(e.g. the independent evolution of swords in Xiphophorus and some
Preference for male dorsal fin size/LPA may be favored by
guppy populations; Basolo, 1995a).
females either through greater stimulation of the female sensory
There are however, several studies of female preference in poe-
system and brain or due to an adaptive reason (Rowland, 1989a;
ciliid fishes that, although not designed to test LPA, produced
Ryan and Keddy-Hector, 1992). The greater response of percep-
results inconsistent with our hypothesis. Some mate preference
tual systems to increased stimulation often leads animals to prefer
experiments, for example, have demonstrated female discrimina-
larger, brighter, or more vigorous mates, particularly in species
tion against male fin elaborations (Basolo, 2002b; Rosenthal et al.,
where mate choice is mediated by visual cues (Rowland, 1989a;
2002; Witte and Klink, 2005; Wong and Rosenthal, 2006; Fisher and
Kirkpatrick and Ryan, 1991). Increased body height in the form of
Rosenthal, 2007; MacLaren and Daniska, 2008). Perhaps preference
a dorsal fin and/or body length in the form of an elongated tail are
for male LPA and/or fin elaborations is an ancestral trait within the
factors that enlarge the area of the retina swept by male images dur-
poeciliid family that has been secondarily lost or altered in some
ing courtship (Endler and Houde, 1995; MacLaren, 2006), perhaps
populations as a result of genetic drift (Rosenthal et al., 2002) or for
favoring the evolution of such traits in males. Once established,
some adaptive reason (e.g. caused females to mate at a suboptimal
the apparent size/LPA preference will be maintained through the
rate, mate with inferior males, or risk mating with heterospecifics;
female preexisting bias as well as Fisherian coevolution (Fisher,
Pfennig, 2000; Hankison and Morris, 2002; Basolo, 2002b; Witte
1930).
and Klink, 2005).
Additionally, female preference for larger male fin and/or
Alternatively, the LPA bias may have evolved independently in
body size may be adaptive in populations where size confers an
the poeciliid species examined. This could suggest parallel evolu-
advantage in intrasexual competition for resources and/or mat-
tion of the preference as hypothesized for male fin elaborations
ing opportunities as observed in numerous poeciliids including
above. Shared preference for increased LPA is consistent with com-
X. variatus (Bisazza et al., 1996), among other heritable fitness
mon ancestry of the sensory/neural systems in P. latipinna, P.
mexicana, P. reticulata, and X. variatus females providing support
Table 2 for the single origin/secondary loss hypothesis. However, the same
Results from experiment III (female preference for male dorsal fin: body size ratio): logic could be used to explain multiple gains of preference in that
mean female strength of preference (SOP) (i.e. time spent in association with the
the system may be conducive to evolving the bias based on homol-
larger-bodied, smaller-finned male-time with the smaller-bodied, larger-finned
male per 10 min test period) in each of 10 treatments (n = 22). Results of paired
ogous genes shared in their sensory/neural systems.
samples t-tests comparing total time (s) females spent in association with the Secondary loss seems a more parsimonious explanation than
larger-finned, smaller bodied vs. smaller-finned, larger-bodied dummy male in each multiple gains of preference since it is arguably far more difficult to
treatment and associated Cohen’s d calculations of the effect size (with 95% confi- gain than to lose a preference. However, given the LPA bias appears
dence interval) related to preference strength (Nakagawa and Cuthill, 2007).
evolutionarily labile even within genera, it is a weak argument at
Treatment Mean SOP (s) t-value p-value Cohen’s d (95% C.I.) best. Further studies of additional poeciliid species are necessary
1 vs. 2 35.3 ± 22.4 1.57 0.130 0.412 (−0.185 to 1.010) before any definitive conclusions can be drawn.
1 vs. 3 −44.2 ± 27.4 −1.61 0.122 − 0.444 (−1.043 to 0.154) Although studies suggest fin and body size preferences are prod-
1 vs. 4 87.9 ± 44.2 1.99 0.060 0.742 (0.131 to 1.353) ucts of a single bias for larger male apparent size or LPA (Haines and
1 vs. 5 36.3 ± 47.6 0.76 0.455 0.276 (−0.318 to 0.869) Gould, 1994; Rosenthal and Evans, 1998; Karino and Matsunaga,
2 vs. 3 −26.8 ± 36.1 −0.74 0.466 −0.257 (−0.851 to 0.336)
2 vs. 4 35.2 ± 38.4 0.92 0.370 0.327 (−0.268 to 0.922)
2002; MacLaren et al., 2004, submitted for publication; MacLaren
2 vs. 5 25.4 ± 39.7 0.64 0.530 0.225 (−0.368 to 0.818) and Rowland, 2006) we cannot rule out the possibility that these
3 vs. 4 −10.5 ± 23.6 −0.45 0.660 −0.188 (−0.709 to 0.474) preferences are independently evolved traits that tap into different
3 vs. 5 −40.0 ± 36.0 −1.11 0.280 −0.392 (−0.989 to 0.204) biases (e.g. separate preferences for male height and ventral body
4 vs. 5 7.1 ± 30.7 0.23 0.820 0.072 (−0.519 to 0.663)
length). The apparent lack of dorsal fin and/or body size preferences

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202 R.D. MacLaren et al. / Behavioural Processes 87 (2011) 197–202
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This study was supported in part by a Merrimack College 1457–1472.
Faculty Development Grant. E. ElAchi, and P. Imbriano offered MacLaren, R.D., Daniska, D., 2008. Female preferences for dorsal fin and body size
valuable assistance in data collection and analysis. C. MacLaren in Xiphophorus helleri: further investigation of the LPA bias in Poeciliid fishes.
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and two anonymous reviewers provided helpful comments on the MacLaren, R.D., Rowland, W.J., 2006. Female preference for male lateral projection
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MacLaren, R.D., Rowland, W.J., Morgan, N., 2004. Female preferences for sailfin and
Texas State University, San Marcos, TX. for supplying the fish used in body size in the sailfin molly, Poecilia latipinna. Ethology 110, 363–379.
this study. The research methods presented herein were described MacLaren, R.D., Fontaine, A., Iacozzi, S., Ash, M., Ash, P. Female preference for male
in Research Protocol 1RDM1008 and approved by the Institutional lateral projection area in Poecilia reticulata, submitted for publication.
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