Alternative life-history styles of Japanese freshwater sculpins revisited

Synopsis Japanese freshwater sculpins consist of 6Cottus and 1Trachidermus species, with various types of life-cycles, namely, catadromous, amphidromous, lacustrine land-locked and fluvial land-locked. Among them,C. amblystomopsis andC. nozawae have been regarded as sibling species. Because of very similar morphological and ecological adult characteristics they were formerly classified as a single species.C. amblystomopsis mainly inhabits the lower courses of rivers and produces many small eggs from which pelagic larvae are formed. In contrast,C. nozawae lives in the middle or upper courses of rivers and deposits few, large eggs, from which well-developed benthic young emerge, well on the way to the definitive phenotype as fully formed juveniles. These two species have distinctly different life-cycles: amphidromous forC. amblystomopsis and fluvial forC. nozawae. A comparison of the early ontogeny shows that, amongCottus species, the small-egg, amphidromousC. amblystomopsis is altricial, while the large-egg, fluvialC. nozawae is precocial. Assuming thatC. nozawae has been derived phylogenetically fromC. amblystomopsis or its ancestral relatives, it is reasonable to consider that the fluvial land-locked life-history style ofC. nozawae has evolved from the ancestral arnphidromous one through adapting to the upstream habitat by an increase in egg size and consequent truncation of the larval period.     

The function of habitat change during brood-rearing in the precocial Kentish plover <Emphasis Type="Italic">Charadrius alexandrinus</Emphasis>

Food availability is often variable during the breeding season. Parents with nonmobile, altricial young have no choice but to accept changes in local food availability, whereas in precocial animals, the parents may lead their young away from poor sites to areas that have rich resources and/or are safe from predators. We investigated the latter hypotheses in the Kentish plover Charadrius alexandrinus, a precocial shorebird that raises its young in two habitats: on lakeshore and in saltmarsh. Parents move with their broods from saltmarsh to lakeshore, especially late in the breeding season, and we hypothesized that lakeshores provide more food than the saltmarsh. Consistent with our hypotheses, plover chicks grew faster on the shore, and the difference in growth rates between the two habitats was amplified later in the breeding season. In addition, brood survival was higher on lakeshore than in saltmarsh and decreased with hatching date. Taken together, our results suggest that Kentish plover parents increase their reproductive success by switching brood-rearing habitats strategically.     

Postnatal allometry of the skeleton in Tupaia glis (Scandentia: Tupaiidae) and Galea musteloides (Rodentia: Caviidae)--a test of the three-segment limb hypothesis

During the evolution of therian mammals, the two-segmented, sprawled tetrapod limbs were transformed into three-segmented limbs in parasagittal zig-zag configuration (three-segment limb hypothesis). As a consequence, the functional correspondence of limb segments has changed (now: scapula to thigh, upper arm to shank, fore arm plus hand to foot). Therefore, the scapula was taken into account in the current study of the postnatal growth of the postcranial skeleton in two small mammalian species (Tupaia glis, Galea musteloides). Comparisons were made between the functionally equivalent elements and not in the traditional way between serially homologous segments. This study presents a test of the three-segment limb hypothesis which predicts a greater ontogenetic congruence in the functionally equivalent elements in fore and hind limbs than in the serially homologous elements. A growth sequence, with decreasing regression coefficients from proximal to distal, was observed in both species under study. This proximo-distal growth sequence is assumed to be ancestral in the ontogeny of eutherian mammals. Different reproductive modes have evolved within eutherian mammals. To test the influence of different life histories on ontogenetic scaling during postnatal growth, one species with altricial juveniles (Tupaia glis) assumed to be the ancestral mode of development for eutherians and one species with derived, precocial young (Galea musteloides) were selected. The growth series covered postnatal development from the first successive steps with a lifted belly to the adult locomotory pattern; thus, functionally equivalent developmental stages were compared. The higher number of allometrically positive or isometrically growing segments in the altricial mammalian species was interpreted as a remnant of the fast growth period in the nest without great locomotor demands, and the clearly negative allometry in nearly all segments in the precocial young was interpreted as a response to the demand on early locomotor activity. Different life histories seem to have a strong influence on postnatal ontogenetic scaling; the effects of the developmental differences are still observable when comparing adults of the two species.     

The comparative reproductive styles of two closely related African minnows (Pseadobarbus afer andP. asper) inhabiting two different sections of the Gamtoos River system

Synopsis Two species of a monophyletic lineage of flexible-rayed redfin minnows,Pseudobarbus afer andP. asper, were studied to establish if there were any significant differences in their reproductive styles. They are sister species with few morphological or meristic differences.P. afer andP. asper are open substrate benthic spawners on coarse bottoms (rocks) and non-guarders of non-adhesive eggs. Their young are photophobic as free embryos. Riverine spawning sites indicated a conservative tendency and represented a phylogenetic constraint as compared to the more variable attributes, such as egg size, which were under environmental control within the limits expressed by the genotype. The combination of life-history attributes, gonadosomatic index, fecundity, egg size, investment per clutch, number of clutches per season and reproductive lifespan was found to be different forP. afer andP. asper. P. asper is derived and atypical of otherPseudobarbus species studied to date. Differences betweenP. afer andP. asper are directly related to the two distinct environments inhabited by these species-coastal Cape Fold Belt mountain streams and the inland Karoo streams of the Gamtoos River system.P. asper may have reverted, by juvenilization, to a more altricial form to survive the turbid, intermittent Karoo stream.     

The proportion of different eco-ethological sections of reproductive guilds of fishes in some African inland waters

Synopsis The continent of Africa has a wide variety of inland waters ranging from rift valley lakes to endorheic and coastal lakes, floodplains and rivers. This paper makes a preliminary comparison of the number of species in different eco-ethological sections of the reproductive guild categories of non-guarders, guarders and bearers in ancient African Great Lakes (Malawi, Victoria and Tanganyika), fluctuating endorheic lakes (Ngami, Chad and Chilwa), typical rivers (Orange-Vaal, Limpopo, Phongolo, Sabi-Lundi, Middle and Lower Zambezi, Kafue, Cunene, Okavango, Niger, Luongo, Lower Zaire) and wetlands (Okavango Delta and Kafue floodplain). The results indicate that the highest percentage of bearers and guarders is found in the ancient African Great Lakes, which are characterised by relatively predictable physico-chemical regimes, whereas a higher percentage of non-guarders is found in the rivers and wetlands, which have less predictable physico-chemical regimes. The management implications of this observation are discussed, and the usefulness of the species as a unit in ecology is assessed.     

Alternative life-history traits associated with reproduction in Oreochromis mossambicus (Pisces: Cichlidae) in small water bodies of the eastern Cape,South Africa

Synopsis Four wild populations of Oreochromis mossambicus were investigated to examine the effects of environmental factors on reproductive biology in contrasting habitats. Age at maturity, spawning-season length, spawning frequency, clutch size and nesting behaviour were influenced by the prevailing conditions for feeding, breeding and refuge. Even under a temperature regime that approached lethal limits during winter, and erratically fluctuating water levels, O. mossambicus demonstrated an ability to adopt a precocial life-history style in some habitats. In more hostile water bodies an increasingly altricial style was followed.     

Life-history styles of fishes in South African estuaries

Synopsis Fish utilizing South African estuaries may be divided into two major groups according to the location of their spawning sites. The marine group comprises large species which spawn at sea, enter estuaries mainly as juveniles, and return to the sea prior to attaining sexual maturity. The estuarine group is dominated by small species which have the ability to complete their life cycle within the estuarine environment. They tend to produce relatively few, demersal eggs, or exhibit parental care, which facilitates the retention of eggs and young within the estuary, whereas the marine group release large numbers of small pelagic eggs during spawning and exhibit no parental care. This is contrary to the theory that estuaries (unpredictable environments) should favour altricial life-history styles and the marine inshore zone (a more predictable environment) should favour precocial styles. However, if the total ichthyofauna of South African estuaries is considered, then altricial species predominate. The fact that both altricial and precocial traits are well represented within the overall estuarine fish community suggests that the various taxa have adapted their life-history styles, in different ways, to ensure the utilization of abundant food resources available within these fluctuating systems. A detailed comparison of the life-history styles of the estuarine teleostGilchristella aestuaria and the marine fishMugil cephalus is used to illustrate the contrasting manner in which these two species have succeeded in exploiting South African estuaries.     

The reproductive biology and early development of the African pike,Hepsetus odoe,in the Okavango Delta,Botswana

Synopsis The reproductive biology of the African pike,Hepsetus odoe, was studied over a four-year period in the Okavango Delta, Botswana. Spawning takes place between August and May in different parts of the Delta. Fish in the seasonal swamp and drainage rivers have a truncated spawning season between August and January, while those in the perennial swamp have an extended spawning season from September to May. The variation in spawning season appears to be associated with the degree of environmental perturbation brought about by the annual flood cycle. Male and female pike mature at 140 and 160 mm standard length (SL) respectively. Females predominate in the population and produce an average of 6440 eggs per season and are multiple spawners. The number of eggs per spawning averages about 2630. The eggs are deposited in a foam nest which is guarded by the parents. Newly hatched embryos suspend themselves below the nest via a cement gland and remain in the vicinity of the spawning site until they have reached a relatively advanced stage in their development. The larval period is relatively short which implies that this species undergoes nearly a direct development. Foam nests appear to be a predator avoidance mechanism as well as an adaptation to fluctuating oxygen and water levels. The initiation of the spawning season is more closely associated with water temperature than with the annual flood cycle which appears to be more important in regulating the size of the spawning stock.     

A comparative study of embryonic development of some bird species with different patterns of postnatal growth

Some studies show that birds with high postnatal growth rates (e.g. altricial species) are characterized by a rapid early development of "supply" organs, such as digestive organs. Birds with low postnatal growth rates (e.g. precocial species) exhibit a slower early development of these organs and a more rapid early development of other "demand" organs, such as brain, muscles, skeleton and feathers. To test whether these differences can be traced back to early embryonic development and whether they can be associated with changes in developmental timing, i.e. heterochrony, we compared embryos of the precocial quail and the altricial fieldfare, two bird species with low and high postnatal growth rates, respectively. We used classical staging techniques that use developmental landmarks to categorize embryonic maturity as well as morphological measurements. These techniques were combined with immune detection of muscle specific proteins in the somites. Our data showed that the anlagen of the head, brain and eyes develop earlier in the quail than in the fieldfare in contrast to the gut which develops earlier in the fieldfare than in the quail. Our data also showed that the quail and the fieldfare displayed different rates of myotome formation in the somites which contribute to muscle formation in the limbs and thorax. We believe these observations are connected with important differences in neonatal characteristics, such as the size of the brain, eyes, organs for locomotion and digestion. This leads us to the conclusion that selection for late ontogenetic characteristics can alter early embryonic development and that growth rate is of fundamental importance for the patterning of avian embryonic development. It also appears that this comparative system offers excellent opportunities to test hypotheses about heterochrony.     

Relationships among rodent taxa as indicated by reproductive biology1

Demonstrated that in rodents the duration of ontogenetic development (from conception to the age of eye openin) is allometrically related to the maternal body weight. The differences between actual developmental time and the expected time (counted for animals of that systematic position and that body weight) can be used as a tool to test phylogenetic relationships. As far as the relationships between sister-taxa are concerned, the results of the present analysis corroborate the conclusions of modern classifications. A long developmental time (which means by implication also a long pregnancy and precocity) is couled with hystricognathy and hystricomorhy. These traits must be considered plesiomorphic and their occurrence suggests conservatism of articular taxa. Parallell (coupled) with adopting sciurognathy and, particularly, protrogomorpiy, sciuromorphy, and eventually, myomorphy, rodents were able to shorten their developmental times. In this way they could increase the reproductive rate and made their reproduction more efficient. Consequently the respective taxa radiated more rapidly and successfully.