Age and growth of two newly established invasive populations of Tilapia mariae in northern Australia

Sagittal otoliths were used to age the samples of Tilapia mariae collected from a coastal river and an impoundment. Validation of sagittae checks was achieved using both quantitative marginal increment analysis and by tetracycline marking of the otoliths of fish kept in tanks and in a farm dam. The annulus pattern on the otoliths was generally clear and their formation appeared to be temperature related and largely completed in the Austral spring around September and October. Male T. mariae grow faster and larger than females and the maximum ages of fish from the coastal river and impoundment was 9+ and 4+ years, respectively. Past fish surveys and the absence of older age classes in the impoundment population would suggest that this population was only very recently established.     

Contrasting Parental Tasks Influence Parental Roles for Paired and Single Biparental Cichlid Fish

Biparental care of young occurs when both parents provide some sort of care for offspring and can include a wide variety of behaviors, yet often studies focus on single aspects of parental care when trying to determine how each parent contributes. Here, we presented the biparental convict cichlid fish (Amatitlania nigrofasciata) with two conflicting parental behaviors: retrieval of non‐swimming offspring that have been displaced from the nest and defense against a conspecific intruder, a potential brood predator. We examined single males, single females, and pairs of parents to determine how males and females each contributed to overall parental care. Traditionally in this species, parents exhibit a division of labor (in which each parent contributes to all parental activities), but also exhibit a division of roles (in which males tend to favor the role of defense and females tend to favor more direct care, spending more time with offspring). We hypothesized that single parents would compensate for their absent mate, but that males and females would still favor preferred roles. Additionally, we hypothesized that there would be an asymmetrical expansion of roles, with females being more flexible. Our results show that the preferred roles of both parents were evident even when parents were without their mates and that males and females differed in their compensatory levels, at least when compared to the behaviors of the intact pair. Contrary to our prediction, females seem unable to fully compensate for the defensive behaviors usually exhibited by males, while males shifted completely to retrieve displaced offspring.     

Lacustrine radiations in African Synodontis catfish

Synodontis catfish are a species‐rich, tropical pan‐African genus that predominately occur in fluviatile environments, but which also form a small radiation within Lake Tanganyika (LT). Here we estimate Synodontis relationships, based on mitochondrial and nuclear DNA, greatly expanding previous sampling. Data were analysed using different methods of phylogenetic inference: Bayesian (also testing compositional heterogeneity), likelihood and parsimony, in order to investigate biogeographic history and the extent of intralacustrine speciation within this group. Bayesian‐relaxed clock analyses were used to estimate timings of radiations. Our analyses reveal a single origin of the LT flock with the inclusion of the nonendemic S. victoriae, and that these taxa evolved relatively recently (5.5 Ma), considerably later than the formation of LT (9–12 Ma). Two internal endemic clades diversified at a similar time (2–2.5 Ma), corresponding to a period of climate change, when lake levels dropped. We find evidence for a further species flock, composed of riverine southern African taxa, the diversification of which is very rapid, 0.8 Ma (95% HPD: 0.4–1.5) and infer a similar scenario for the diversification of this flock to southern African serrachromine cichlids in that they radiated in the now extinct lake Makgadikgadi. We also reveal that the biogeographic history of Synodontis catfish is more complex than previously thought, with nonmonophyletic geographic species groupings.     

Influence of prey foraging posture on flight behavior and predation risk: predators take advantage of unwary prey

Foraging in animals is often associated with characteristicbody postures, such as the head-down posture. When foragingconflicts with the ability to detect predators or to flee, individualsmay incur a greater risk of mortality to predation than otherwise.Here we investigate the influence of different foraging postures(horizontal versus nose-down body posture) on the ability ofindividuals to respond to approaching predators and on the riskof mortality to predation in the guppy (Poecilia reticulata).Individuals engaged in nose-down foraging were assumed to beable to visually scan a smaller area for predators and to escapeless effectively due to their body posture, and thus are morevulnerable to stalking predators than horizontally foragingones. In a first experiment, we separately exposed nonforaging,horizontally foraging, and nose-down foraging guppies to anapproaching cichlid fish predator model. Nonforaging guppiesreacted sooner to and initiated flight further away from theapproaching model than did foraging fish collectively, and horizontallyforaging individuals responded sooner to the model than nose-downforaging ones. Comparing all test guppies, nose-down foragingindividuals were the most likely not to exhibit any responseto the predator model. When presented with a simultaneous choiceof two guppies behind a one-way mirror, individual blue acaracichlid (Aequidens pulcher), a natural predator of the guppy,preferred to attack foraging guppies over nonforaging ones andnose-down foraging guppies over horizontally foraging individuals.In a final experiment with free-swimming cichlids and guppies,we demonstrated that individual risk of predation for guppiesforaging nose down was greater than for guppies foraging horizontally,and both were at greater risk than nonforaging guppies. Thislatter result is consistent with the above differences in theguppy's responsiveness to approaching predators depending ontheir foraging behavior, and with the finding that cichlid predatorspreferred fish that were less likely to show any response tothem. Our results therefore indicate that the ability to respondto approaching predators and the risk of mortality to predationin the guppy is strongly influenced by their foraging activity,and in particular their foraging posture, and that cichlid predatorspreferentially select less wary and more vulnerable guppies.[BehavEcol 7: 264–271 (1996)]     

DISTINCT EVOLUTIONARY PATTERNS OF BRAIN AND BODY SIZE DURING ADAPTIVE RADIATION

Morphological traits are often genetically and/or phenotypically correlated with each other and such covariation can have an important influence on the evolution of individual traits. The strong positive relationship between brain size and body size in vertebrates has attracted a lot of interest, and much debate has surrounded the study of the factors responsible for the allometric relationship between these two traits. Here, we use comparative analyses of the Tanganyikan cichlid adaptive radiation to investigate the patterns of evolution for brain size and body size separately. We found that body size exhibited recent bursts of rapid evolution, a pattern that is consistent with divergence linked to ecological specialization. Brain weight on the other hand, showed no bursts of divergence but rather evolved in a gradual manner. Our results thus show that even highly genetically correlated traits can present markedly different patterns of evolution, hence interpreting patterns of evolution of traits from correlations in extant taxa can be misleading. Furthermore, our results suggest, contrary to expectations from theory, that brain size does not play a key role during adaptive radiation.     

Effects of loss of male parent on brood survival in a biparental cichlid fish

Synopsis When brood-guarding males of the biparental convict cichlid, Cichlasoma nigrofasciatum, held in experimental ponds, deserted their mate and brood, or were removed from the pond, survival of the young depended on their age when the father left. If they were embryos or free embryos, few broods survived, but if they were up to seven days into the free-swimming juvenile period, most broods survived. The cause of brood mortality is not certain, but predation by conspecifics is most likely (no other fish species were in the ponds). The willingness of a deserted, brood-guarding female to continue defending her young probably depends, in part, on their age. If they are very young, the benefit/cost ratio of guarding them to independence may be so low that she should give up that breeding attempt and begin another. If they are older, the benefit/cost ratio is higher and she should continue to guard them alone.     

Punctuated equilibria, morphological stasis and the palaeontological documentation of speciation: a biological appraisal of a case history in an African lake

The present-day faunas of the great African lakes present some of the world's best examples of 'explosive speciation'. Lakes Victoria and Malawi each probably have several hundred endemic species of cichlid fishes. Much can be inferred about the evolution of these fishes from morphology, behaviour and intra-lacustrine distribution and from the fact that they include taxa ranging from local races, through sibling species, to forms that display extensive differentiation. The time taken to acquire specific distinctness can sometimes be accurately defined, but fossil lineages are unknown. A recent study of a fossil sequence of molluscs in the Turkana basin throws new light on the history of African lake faunas. It also claims to have resolved events during speciation. While critical analysis based on our knowledge of living molluscs in this area fails to substantiate this claim, the fossil molluscs complement information provided by the biology of extant fishes and invertebrates and emphasize the importance of these lakes in the study of evolution in living and extinct populations.     

A sympatric sibling species complex of Petrotilapia Trewavas from Lake Malawi analysed by enzyme electrophoresis (Pisces: Cichlidae)

The protein electromorphs of three taxa of Petrotilapia , referred to in earlier works as sibling species, were examined by starch-gel electrophoresis. The results indicated that, for the three taxa, no alternative fixed alleles occurred for any of the 25 loci (enzymes) examined. However, heterogeneous gene frequencies were indicated at seven polymorphic loci. This suggests that either the taxa are isolated 'sibling' species which recently diverged, or that they are 'incipient' species with minimal gene flow between morphs. The genetic and field data lend support to the hypothesis that sympatric splitting of morphs could be important in the explosive radiation of the cichlidae.     

Lunar synchronization of spawning in cichlid fishes of the tribe Lamprologini in Lake Tanganyika

Lunar synchronization of spawning was investigated for eight substrate brooding cichlid fishes belonging to the tribe Lamprologini. Their spawning activities all peaked during the second quarter of the lunar cycle. Comparison between their breeding styles and the degrees of spawning synchronization suggested that the nocturnal guarding-efficiency of eggs, especially exposed ones, is improved by the maximal amount of moonlight during full moon and, in species whose young leave the breeding sites about 2 weeks after spawning, the survival of dispersing young is enhanced by the darkness of moonless nights.     

Probing aggressive motivation in a cichlid fish

The duration of startles provides an inverse measure of motivation to resume the previous activity. Here, we use a novel method in which one convict cichlid fish (Amatitlania nigrofasciata) of a competing pair was startled independently of the opponent. Fish were given various opponents and the mean startle duration determined. This mean was negatively correlated with the mean use of highly escalated ‘frontal activities’ such as biting and frontal display, but not the less escalated lateral displays or tail beating. Thus the startle duration was a reliable surrogate measure of the most escalated components of aggressive interactions. That is, it provided a motivational probe for aggressiveness of individual fish. Fight motivation is often determined in terms of fight duration or physiological costs for losers, who reveal the costs they are prepared to pay. We discuss various potential advantages of the motivational probe over previous measures, particularly with respect to winners and losers and different times during the interactions.