We investigated the preference of Cave molly males to associate with a receptive or a non-receptive female while body contact was prevented but water-borne cues were allowed to reach the male. Both in light and in darkness, males did not prefer the receptive female. Water-borne chemical cues (pheromones) seem to be absent or they are not detected/used by males, respectively.Istraživali smo način na koji mužjak špiljske ribe Poecilia mexicana odabire receptivnu odnosno nereceptivnu ženku, pri čemu je tjelesni kontakt bio onemogućen, ali su čimbenici nošeni vodom mogli doprijeti do mužjaka. Niti na svjetlu niti u tami mužjaci nisu preferirali receptivne ženke. Proizlazi da vodom nošenih tvari (feromona) nema, ili ih mužjaci ne raspoznaju, odnosno ne koriste

J. Parzefall

K. Wiedemann

M. Plath

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short communication / kratko priop}enjeCAVE MOLLY MALES (POECILIA MEXICANA)DO NOT RECOGNISE RECEPTIVE FEMALESWITHOUT BODY CONTACTMARTIN PLATH*, KARSTEN WIEDEMANN & JAKOB PARZEFALLBiozentrum Grindel und Zoologisches Museum,University of Hamburg, Martin-Luther-King Platz 3,20146 Hamburg, GermanyPlath, M., Wiedemann, K. & Parzefall, J.: Cave molly males (Poecilia mexicana) do not recog-nise receptive females without body contact. Nat. Croat., Vol. 13, No. 2., 197–200, 2004, Zagreb.We investigated the preference of Cave molly males to associate with a receptive or a non-re-ceptive female while body contact was prevented but water-borne cues were allowed to reach themale. Both in light and in darkness, males did not prefer the receptive female. Water-borne chemi-cal cues (pheromones) seem to be absent or they are not detected/used by males, respectively.Key words: Poeciliidae, sexual cycle, pheromones, cave fishPlath, M., Wiedemann, K. & Parzefall, J.: Mu`jaci ribe Poecilia mexicana ne raspoznajureceptivne `enke bez tjelesnog kontakta. Nat. Croat., Vol. 13, No. 2., 197–200, 2004, Zagreb.Istra`ivali smo na~in na koji mu`jak {piljske ribe Poecilia mexicana odabire receptivnu odnosnonereceptivnu `enku, pri ~emu je tjelesni kontakt bio onemogu}en, ali su ~imbenici no{eni vodommogli doprijeti do mu`jaka. Niti na svjetlu niti u tami mu`jaci nisu preferirali receptivne `enke.Proizlazi da vodom no{enih tvari (feromona) nema, ili ih mu`jaci ne raspoznaju, odnosno nekoriste.Klju~ne rije~i: Poeciliidae, spolni ciklus, feromoni, {piljske ribeINTRODUCTIONThe colonisation of lightless subterranean habitats requires that all behaviourpatterns must be released by non-visual cues. In the context of reproductive behav-NAT. CROAT. VOL. 13 No 2 197¿200 ZAGREB June 30, 2004Croatian Natural History Museum, Demetrova 1, Zagreb, Croatia* corresponding author’s e-mail address: mplath@zimserver.zoologie.uni-hamburg.deiour, this means that potential mating partners can only be detected by using chem-ical, acoustical, vibrational/tactile or electro-sensitive senses.The cavernicolous population of the Atlantic molly (Poecilia mexicana Steindachner1863) offers a unique tool to study sensory and behavioural adaptations of a for-merly surface dwelling, diurnal species to life in darkness (PARZEFALL, 2001; PLATHet al., 2004). The Cave molly inhabits a dark sulphurous limestone cave in SouthMexico (GORDON & ROSEN, 1962).In viviparous fishes (Poeciliidae), females have a sexual cycle and Cave molly fe-males become receptive for roughly 2–3 days per month (PARZEFALL, 1973). Malestouch the female gonopore before attempting to copulate, thereby achieving infor-mation concerning gender and a female’s stage in the sexual cycle (PARZEFALL,1973). Receptive females are most attractive for males (PARZEFALL, 1973). However,molly males almost constantly try to mate with any available female.Previous studies have suggested that males need direct body contact to obtainthe necessary chemical information (ZEISKE, 1968). In the present paper, we testedthis hypothesis. Do males prefer to associate with receptive females on the basis ofwater borne far-field signals (chemical cues) when they cannot nip at the femalegonopore?METHODSTest fish came from light reared laboratory stocks of Cave mollies originatingfrom the hindmost isolated cave chamber of the Cueva del Azufre in Tabasco, Mex-ico (chamber XIII after GORDON & ROSEN, 1962; PLATH et al., 2003). Fish were main-tained as randomly outbred large aquarium stocks at the Biozentrum Grindel inHamburg in several tanks of 100–200 l at a temperature of 25–30 °C under a 16:8hour light-dark regime.To determine the receptivity of the stimulus females, three females were housedin 25 l aquaria with one male for two months. We daily counted a male’s nippingfrequency for each female during five minutes. Nipping frequency increased ap-proximately each 28 days when females became receptive (PARZEFALL, 1973).In the choice tests, males were given the opportunity to associate with a recep-tive female and a non-receptive female, matched for size, which were confined towire mesh cylinders (12 cm diameter, 5 mm mesh-width, 1 mm wire-diameter). Thecylinder material allowed non-visual cues from the females to pass through (PLATHet al., 2004). Cylinders were placed in the two outer preference zones (1/3 of thetank) of a test tank (100  35  35 cm), filled up to 2/3 with aged tap-water of 28–30 °C(Fig. 1). The bottom was covered with black gravel.When the two stimulus females were swimming calmly in their cylinders, amale was gently introduced into the central neutral zone. We measured the timethe male spent in both preference zones during 10 minutes. Then, the positions ofthe cylinders were reversed and measurement was repeated. Times from both partsof a trial were added. We decided a priori to exclude trials in which the males spentmore than 80 % of their time in only one preference zone as side biases and trialswith low response (<50 % time spent in the preference zones).198 Plath, M. et al.: Determination of the sexual cycle in Cave molliesSeven side biases occurred. In neither case trials had to be discarded due to lowresponse. We tested for differences in the association times near either males usingpaired t-tests.Cave mollies still posses functional eyes (PETERS et al., 1973). Hence, we tried todetect whether visual cues from the females provide additional information about fe-males’ receptiveness. Therefore, experiments were carried out both in darkness (two500 W infrared bulbs 28 cm above the test tank; Fig. 1) and in light (the test tank wasilluminated by two 60 W incandescent bulbs) in random order. Cave mollies do notsee in the infrared (KÖRNER 1999; KÖRNER et al. in prep.). During the tests in light, theobserver was sitting quietly approximately 2 m from the test tank. During the tests indarkness, the trials were recorded by an infrared-sensitive camera and monitored ina neighbouring room, where trials were scored directly (PLATH et al., 2004).RESULTSIn light males did not discriminate between receptive and non-receptive females(paired t-test: t=0.43, n=11, p=0.67, power=0.05). They spent 52.43±18.57 % of theirtime near the receptive female and 47.57±18.57 % near the non-receptive female.Males also showed no preference in darkness (paired t-test: t=–0.60, n=11, p=0.56,power=0.05). They spent 48.55±8.02 % of their time with the receptive female and51.45±8.02 % near the non-receptive female. In both experiments only five of 11males spent more time near the receptive female.DISCUSSIONOur study confirms the assumption that near-field communication plays a majorrole in the mating behaviour of Cave mollies (ZEISKE, 1968; PARZEFALL, 1970). How-ever, seven trials had to be discarded due to side bias. Hence, sample sizes are rela-Nat. Croat. Vol. 13(2), 2004 199incandescentbulbinfraredbulbFig. 1. Experimental set-up. For details see text.tively small in this study, resulting in low power of the statistical analyses and theresults are discussed with caution.Cave molly males obtain information concerning gender when they nip at the fe-male gonopore before copulating (PARZEFALL, 1973). Sex recognition appears to beimpossible when the male cannot touch the female (PLATH et al., 2003). Males canalso determine a female’s sexual attractiveness when nipping (PARZEFALL, 1973).Here, we demonstrate that female receptiveness cannot be determined by males onthe basis of non-visual (i.e. chemical or water displacement) cues. The high H2Scontent of the water inside the cave may make chemical communication via waterborne pheromones impossible. Furthermore, Cave mollies occur at high density insome parts of the cave and often gather in shallow areas. Selection pressure to im-prove the ability of far-field recognition of female receptiveness might be low, be-cause males can attempt to touch neighbouring fish. Even in light, no discrimina-tion was found, indicating that visual cues do not indicate females’ receptiveness.ACKNOWLEDGEMENTSWe thank the Mexican Government for issuing permits (242.–2190 276/36;210696–213–03). A. K. Pati, C. Lamptey, I. Schlupp and M. Rohde kindly read anearlier version of the manuscript. A. Taebel-Hellwig, T. H. Dirks, I. D. Schmidt andthe aquarium team in Hamburg provided technical support and animal care. Ourexperiments comply with the current laws in Germany.Received February 12, 2004REFERENCESGORDON, M. E. & D. E. ROSEN, 1962: A cavernicolous form of the poeciliid fish Poeciliasphenops from Tabasco, Mexico. Copeia 1962, 360–368.KÖRNER, K. E., 1999: Zur sexuellen Selektion höhlenlebender Atlantikkärpflinge (Poeciliamexicana Steindachner 1863). PhD thesis, University of Hamburg.PARZEFALL, J., 1970: Morphologische Untersuchungen an einer Höhlenform von Mollienesiasphenops (Pisces, Poeciliidae). Zeitschrift für Morphologie der Tiere, 68, 323–342.PARZEFALL, J., 1973: Attraction and sexual cycle of Poeciliids. Pp 177–183 in: SCHRÖDER, J. H.ed. Genetics and mutagenesis of fish. Springer Berlin, Heidelberg, New York.PARZEFALL, J., 2001: A review on morphological and behavioural changes in the cave mollyPoecilia mexicana from Tabasco, Mexico. Environmental Biology of Fishes, 50, 263–275.PETERS, N., PETERS, G., PARZEFALL, J. & H. WILKENS, 1973: Über degenerative und konstruktiveMerkmale bei einer phylogenetisch jungen Höhlenform von Poecilia sphenops (Pisces,Poeciliidae). Internationale Revue der gesamten Hydrobiologie 58, 417–436.PLATH, M., WIEDEMANN, K., PARZEFALL, J. & I. SCHLUPP, 2003: Sex recognition in surface andcave dwelling male Atlantic mollies Poecilia mexicana (Poeciliidae, Teleostei). Behaviour140, 765–782.PLATH, M., PARZEFALL, J., KÖRNER, K. E. & I. SCHLUPP, 2004: Sexual selection in darkness? Fe-male mating preferences in surface- and cave-dwelling Atlantic mollies, Poecilia mexicana(Poeciliidae, Teleostei). Behavioural Ecology and Sociobiology 55, 596–601.ZEISKE, E., 1968: Prädispositionen bei Mollienesia sphenops (Pisces, Poeciliidae) für einenÜbergang zum Leben in subterranen Gewässern. Zeitschrift für vergleichende Physiologie,58, 190–222.200 Plath, M. et al.: Determination of the sexual cycle in Cave mollies

Mužjaci ribe Poecilia mexicana ne raspoznaju receptivne ženke bez tjelesnog kontakta

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