Steven R. Telford

Dishonest signalling in a fiddler crab

Animal communication theory predicts that low–frequency cheating should be common in generally honest signalling systems. However, perhaps because cheats are designed to go undetected, there are few examples of dishonest signals in natural populations. Here we present what we believe is the first example of a dishonest signal which is used commonly by males to attract mates and fight sexual rivals. After losing their large claw, male fiddler crabs (Uca annulipes) grow a new one which has less mass, is a less effective weapon and costs less to use in signalling than an equivalent–length claw of the original form. Males with original claws do not differentially fight males with regenerated claws even though they are likely to win. Regenerated claws effectively bluff fighting ability and deter potential opponents before they fight. During mate searching, females do not discriminate against males with low–mass, regenerated claws, indicating that they are deceived as to the true costs males pay to produce sexual signals. Up to 44% of males in natural populations have regenerated claws, a level unanticipated by current signalling theory. The apparent rarity of cheating may be an artefact of the usual difficulty of detecting cheats and dishonesty may be quite common.

Life-history phenotypes in populations of Brachyrhaphis episcopi (Poeciliidae) with different predator communities

Abstract. Variation among populations in extrinsic mortality schedules selects for different patterns of investment in key life-history traits. We compared life-history phenotypes among 12 populations of the live-bearing fish Brachyrhaphis episcopi. Five populations co-occurred with predatory fish large enough to prey upon adults, while the other seven populations lacked these predators. At sites with large predatory fish, both sexes reached maturity at a smaller size. Females of small to average length that co-occurred with predators had higher fecundity and greater reproductive allotment than those from populations that lacked predators, but the fecundity and reproductive allotment of females one standard deviation larger than mean body length did not differ among sites. In populations with large predatory fish, offspring mass was significantly reduced. In each population, fecundity, offspring size and reproductive allotment increased with female body size. When controlling for maternal size, offspring mass and number were significantly negatively correlated, indicating a phenotypic trade-off. This trade-off was non-linear, however, because reproductive allotment still increased with brood size after controlling for maternal size. Similar differences in life-history phenotypes among populations with and without large aquatic predators have been reported for Brachyrhaphis rhabdophora in Costa Rica and Poecilia reticulata (a guppy) in Trinidad. This may represent a convergent adaptation in life-history strategies attributable to predator-mediated effects or environmental correlates of predator presence.

MATE CHOICE OCCURS ONLY IN SMALL CHORUSES OF PAINTED REED FROGS HYPEROLIUS MARMORATUS

ABSTRACT In two-choice discrimination experiments, females of Hyperolius marmoratus preferred the calls of lower frequency of the pair of stimuli. This preference was not shown in mating patterns observed in natural choruses, but is when females are phonotactically orienting in small choruses in an experimental enclosure. With an increase in chorus size, the mating pattern shifts from size-based, non-random (with some evidence of size-assortative) mating to random mating. This is the first time that frequency-based mate-choice by female anurans has been associated with chorus size, and hence with the sonic complexity of the acoustic environment.

Establishing cryptic female choice in animals

Previous research has focused on biased fertilization by males from the same genetic strain as the female or by conspecifics over heterospecifics. In flour beetles (Tribolium castaneum), black strain males had lower P2 (the proportion of eggs fertilized by the second male when females are doubly mated) values than wild-type males when they were the second mates of wild-type females, although both male types achieved similar values when mated to black strain females[9xSources of intraspecific variation in sperm precedence in red flower beetles. Lewis, S.M and Austad, S.N. Am. Nat. 1990; 135: 351–359Crossref | Scopus (121)See all References[9]. In the grasshoppers Chorthippus parallelus and Podisma pedestris, reciprocal crosses between two geographic races generated fewer hybrids than expected in one race of the former species and in both races of the latter[12xSperm precedence and homogamy across a hybrid zone in the Alpine grasshopper Podisma pedestris. Hewitt, G.M, Mason, P, and Nichols, R.A. Heredity. 1989; 62: 343–353Crossref | Scopus (6)See all References, 13xAsymmetrical homogamy and unequal sex ratio from reciprocal mating-order crosses between Chorthippus parallelus subspecies. Bella, J.L et al. Heredity. 1992; 68: 345–352Crossref | Scopus (68)See all References]. Similarly, in ground crickets (Allonemobius spp.), doubly mated females preferentially fertilized eggs with conspecific sperm, regardless of the order in which males were mated[14xA post-insemination barrier to fertilisation isolates two closely related ground crickets. Gregory, P.G and Howard, D.J. Evolution. 1994; 48: 705–710CrossrefSee all References[14]. The most convincing evidence for a female role comes from new work on Drosophila[15xConspecific sperm precedence in Drosophila. Price, C.S.C. Nature. 1997; 388: 663–666Crossref | PubMed | Scopus (126)See all References[15], where females of three species all preferentially use conspecific sperm. This conclusion was not confounded by differential mortality of hybrid and pure-bred offspring.More importantly, it was also shown that P2 values, which tend to be uniformly high for conspecific double-matings of both Drosophila simulans and Drosophila mauritania, are highly variable when two D. mauritania males mate with a D. simulans female. Interactions between the sperm of two conspecific males, therefore, depend on female-mediated processes, and consistently high P2 values cannot be attributed solely to male sperm displacement or mechanical constraints on the manner of sperm storage by females.

Breeding phenology, variation in reproductive effort and offspring size in a tropical population of the woodlouse Porcellionides pruinosus

SummaryMost species of woodlice in temperate habitats have discrete breeding seasons. It is hypothesised that breeding synchronises with favourable environmental conditions to maximise offspring growth and survivorship (Willows 1984). We measured the breeding phenology of a species introduced to a tropical environment, primarily to consider the assumption that life histories in the tropics will differ fundamentally from those in temperate habitats. In addition to breeding phenology we considered variation in reproductive effort between individual females and the division of this effort between the size and number of young.A continuous breeding phenology was observed in a synanthropic population of Porcellionides pruinosus within the tropics. Reproductive effort varied between months, showed a weak relationship with female size and was independent of female fecundity. Female sizefecundity relationships varied between samples and when the proportion of reproductive females was high size-fecundity slopes were steeper than at other times. Mean offspring size varied between months and there was a wide range in offspring size within broods. Offspring size was not related to female body mass, reproductive effort or fecundity; consequently brood mass increased linearly with an increase in fecundity. Increased reproductive effort goes into more rather than larger offspring.We propose that the continuous breeding in this population was the result of the constant presence of an environmental cue to reproduction evolved in temperate habitats. Continuous breeding is not necessarily equivocal to high individual reproductive success even though overall population growth may be rapid. However, variation in reproductive effort suggests that individuals respond to current environmental conditions on short time scales.

Manipulation of the sex ratio and duration of copulation in the tropical millipede Alloporus uncinatus : a test of the copulatory guarding hypothesis

Bailey, W. J. & Yeoh, P. B. 1989. Female phonotaxis and frequency discrimination in the bushcricket Requena verticalis (Tettigoniidae: Listrocelidinae). Physiol. Entomol., 13, 363-372. Gwynne, D. T. 1988. Courtship feeding and the fitness of female katydids (Orthoptera: Tettigoniidae). Evolution, 42, 545-555. Latimer, W. 1981. Variation in the song of the bush cricket Platyeleis albopunctata (Orthoptera: Tettigoniidae). J. nat. Hist., 15, 245-263. Latimer, W. & Schatral, A. 1986. Information cues used in male competition by Tettigonia cantans (Orthoptera: Tettigoniidae). Anim. Behav., 34, 162-168. Latimer, W. & Sippel, M. 1987. Acoustic cues for female choice and male competition in Tettigonia cantans. Anita. Behar., 35, 88%900. Michelsen, A. 1985. Environmental aspects of sound communication in insects. In: Acoustic and Vibrational Communication in h~sects (Ed. by K. Kalmring & N. Elsner), pp. 1-10. Berlin: Paul Parey. Partridge, L., Hoffmann, A. & Jones, J. S. 1987. Male size and mating success in Drosophila melanogaster and D. pseudoobscura under field conditions. Anim. Behav., 35, 468-476. Simmons, L. W. 1988. Male size, mating potential and lifetime reproductive success in the field cricket Gryllus bimaculatus (De Geer). Anim. Behav., 36, 372-379. Steele, R. H. & Partridge, L. 1988. A courtship advantage for small males in Drosophila subobscura. Anita. Behav., 36, 1190-1197. Wiley, R. H. & Richards, D. G. 1978. Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations. Behav. Ecol. Sociobiol., 3, 69-94.

The effect of rainfall on interclutch interval in painted reed frogs (Hyperolius marmoratus)

Body size, frequency of mating, clutch size, hatching success, and interval between successive matings were determined during 1982 and 1983 for a population of painted reed frogs, Hyperolius marmoratus , in southern Africa. Females mated once or twice during a single breeding season, which lasted 4 mo. Larger females produced larger egg clutches and had a greater probability of breeding twice. Absolute clutch size varied considerably, though hatching success was uniformly high and not related to the body sizes of mated pairs or the ability to produce more than one clutch. The interval between successive matings, 15-105 d, was dependent on the amount of rain prior to oviposition. Apparently females have some control over time of mating and oviposition in relation to rainfall patterns.

Sexual selection in an African toad (Bufo gutteralis): the roles of morphology, amplexus displacement and chorus participation

Males employed two reproductive tactics: amplexus displacement and vocal advertisement. Outcomes of amplexus displacement attempts could be predicted from body sizes of competing males alone. Mating was non-random and size-selective, but not sizeassortative. There was no evidence of female choice based on male body size. Male mating success and body size were positively correlated, although the relationship between success and multiple size measures was complex. There was no trend, over a sequence of chorus nights, in the total number of males calling, but larger males generally entered the breeding assemblages earlier and participated in more choruses. After entering their first chorus, males tended to call for an unbroken sequence of nights. Males entering the most choruses achieved the most matings. There was a weak negative correlation between time spent calling and mating success, and the mean duration of calling events was less for those that led to mating than for those that did not; these results may well have been due to the large proportion of matings achieved through amplexus displacement rather than vocal advertisement. The major proximate mechanisms contributing to the mating system relate to chorus participation; larger males arrived at the breeding site first, participated in more choruses, and achieved the greatest number of matings. The advantage enjoyed by large males in the amplexus displacement process may have been the ultimate determinant of their mating success, especially since female choice was not size-selective.

Mating Tactics in the Tropical Millipede Alloporus Uncinatus (Diplopoda: Spirostreptidae)

Field and laboratory observations of mating behaviour in a population of the tropical millipede Alloporus uncinatus were carried out over one breeding season. Males obtained mates through random encounters and by forming triplet associations with copula pairs. The occurrence of triplet associations in the field was coincident with a highly male biased operational sex ratio. Mate acquisition by males was apparently stochastic and direct physical competition did not occur. In laboratory experiments mating was size-selective probably as a consequence of female choice. We consider the possibility that sperm competition has contributed to the evolution of the mating system in this species.

Some Determinants of the Mating System in a Population of Painted Reed Frogs (Hyperolius Marmoratus)

Hyperolius marmoratus shares its breeding site with 12 synchronously breeding species. Males call from elevated perches to attract females. Observations of captive populations suggest that males may adopt alternative mating strategies when chorus densities are high. Similar strategies were not observed in natural choruses. The operational sex ratio (OSR) was always male-biased and also highly variable. Mating was polygynous, only 25% of the male population actually mated. Females mated either once or twice. Variance in mating success was much greater among males, an obvious consequence of a skewed OSR. Female choice was probably not a causal factor because male mating success was correlated with neither size nor age. Size-based variation in the male advertisement call does exist, but females cannot exploit this potential vocal cue because of their impaired discriminatory ability in a complex sonic environment and the potential risk of mismating. Although the mating system may best be described as lek-like, with males forming organised choruses through competitive interactions, the variance in male mating success is probably a consequence of stochastic factors.