The evolution of redd site selection in brook charr in different environments: same cue,same benefit for fitness*

1. Despite the great interest in characterising fish reproductive habitat, the relationship between the selection of a given spawning site and individual fitness has not been experimentally tested. 2. In this study, we used an in situ experimental approach to determine (i) the relative contribution of substrate characteristics as well as hydrological and physicochemical variables to small‐scale redd site selection by brook charr, Salvelinus fontinalis (Mitchill) and (ii) if hatching and emergence success, used as a surrogate of fitness, are improved in selected compared to non‐selected sites in both lake and stream habitats. 3. Our results show that upwelling groundwater flow was always significantly higher in selected than in non‐selected sites in both lake and stream habitats. We found no significant difference in the mean geometric substrate diameter and no consistent differences in substrate composition between selected and non‐selected sites. Oxygen concentration was higher (significantly so in three of four comparisons) and conductivity tended to be lower in selected than in non‐selected sites, while temperature showed no significant or consistent variations. We found a significant positive relationship between the selection of a given spawning habitat and hatching and emergence success in these systems. 4. These results show that the main cue that brook charr use to select their spawning sites is upwelling groundwater in lake and stream habitats, and that active selection of these sites increases individual fitness. This suggests that natural selection acted on the same cues in lentic and lotic environments; this could have been highly adaptive in a species that used both habitats as colonisation routes after the last glaciation.     

Storage tissue metabolism and reproduction in marine bivalves—a brief review

Summary

The diversity of storage tissue cell types in bivalve molluscs is evident. In some species there are no specific storage cells, and the adductor muscle plays the role of a reserve tissue (Pectinidae). In others both muscular cells and specific storage cells are involved in storage and release of nutrients for gametogenesis (Veneridae). A few species have a specific storage tissue such as the mantle in Mytilus containing two complementary types of cells. This specialisation can be correlated with the fertility of the species and with the variation of available food organisms. Vesicular connective tissue is found in species with a high level of fecundity which are subject to marked fluctuations in food availability (Mytilidae, Ostreidae). This can be considered as an adaptive behaviour to profit from uncertain supply of food supplies in order to produce the maximum number (and quality) of gametes in a precise period of the year.     

Endocrine Bases of Spatial and Temporal Opportunism in Arctic-Breeding Birds

The primary objectives of this paper are to define, explorethe environmental factors favoring, and discuss hypotheses concerningthe endocrine bases of two important arctic breeding strategiesthat we call spatial and temporal opportunism. We identify severalspecies that display spatial opportunism in the Arctic, andone that displays temporal opportunism. In spatial opportunism,breeding may be highly seasonal but the locality where individualsbreed may change from year to year as a result of unpredictablespatial distribution of food, nest site availability, or otherfactors such as predator abundance. We suggest that flexibilityof the transition from migration to settlement distinguishesspatial opportunists from site-faithful migrants. Thus far,data are available for only two hypotheses regarding the endocrinebasis of this flexibility. Circulating patterns of testosterone(associated with territory establishment) and corticosterone(associated with migratory activity) appear not to be involvedin the regulation of spatial opportunism in white-crowned sparrows(Zonotrichia leucophrys gambelii), but more detailed study isnecessary. In temporal opportunism (that may occur simultaneouslywith spatial opportunism), temporally variable food availabilityapparently selects for the capacity to initiate reproductionacross a wide portion of the year. Tonic activity of the hypothalamo-pituitary-gonad(HPG) axis could provide a mechanism to minimize the delay betweendiscovery of abundant food and onset of nesting in any season.However, the evidence for one arctic temporal opportunist, thewhite-winged crossbill (Loxia leucoptera), indicates that theHPG axis is not tonically active, but probably switches off(i.e., becomes photorefractory) in autumn, as for other birdsbreeding at these latitudes. Opportunistic breeding very earlyin the year (e.g., March near Fairbanks, Alaska) is associatedwith increased luteinizing hormone secretion, probably in responseto a combination of abundant food and social stimuli, afterrefractoriness dissipates. We have taken the first step of identifyingspatial and temporal opportunism as important phenomena in theArctic, and discussing hypotheses related to endocrine mechanisms.Future research should identify specific environmental cuesinvolved, and elucidate the neuroendocrine and endocrine mechanismsunderlying these two reproductive strategies.     

Short- and long-term advantages of an alternative ontogenetic pathway

We documented hypotheses on the evolution of developmental heterochronies by estimating short- and long-term advantages of alternative morphs. In this respect, we compared food energy intakes and body condition between paedomorphic and metamorphic Alpine newts ( Triturus alpestris , Caudata, Amphibia) in four populations. Because we found a strong correlation between fat reserves and body condition, we used this last parameter as an indicator of long-term gains. In all studied sites, paedomorphic females showed higher body condition than metamorphic ones. Paedomorphic males were also at advantage in two populations. Paedomorphs exhibited higher energy intakes than metamorphs in two populations and similar gains in two others. Our results support unifying theories that predict the occurrence of facultative paedomorphosis in varied habitats as paedomorphs exhibited better energy balance than metamorphs. This work shows the need for considering integrative parameters such as body condition in the comparative study of performances when studying developmental heterochronies. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 105–112     

Cash, Color, and Colonialism: The Politics of Tribal Acknowledgement

Cash, Color, and Colonialism: The Politics of Tribal Acknowledgement. Reneé Ann Cramer. Norman: University of Oklahoma Press, 2005. 234 pp.     

Fur seal mothers memorize subsequent versions of developing pups’ calls: adaptation to long‐term recognition or evolutionary by‐product?

In pinnipeds and especially in otariids, mothers and pups develop the capacity to recognize each other's voices. Pups become able to discriminate their mother's voice a few days after birth. For females, this discrimination seems to occur earlier, probably during the few hours after parturition. However, during lactation, mothers are confronted with a major problem: the change of the characteristics of their pup's calls. To investigate this problem, we first performed an acoustic analysis of pups' calls from birth to weaning to identity the successive different versions of these calls. Secondly, we performed playback experiments just before weaning to test if females retain these different versions over a long time period. The acoustic analysis of pups' calls reveals that several characteristics of their vocalizations change with age. Playback experiments demonstrate that females still recognize all the successive immature and mature versions of their pup's calls. In our opinion, this long-term memorization seems to be a by-product of the permanent pups' voice learning from birth to weaning since no apparent adaptive benefit seems to arise from this capacity.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 305–312.     

Nine polymorphic microsatellite markers in Crepis sancta (Asteraceae)

We describe nine new variable di‐ and trinucleotide microsatellites in the plant Crepis sancta, as well as conditions for multiplexing and simultaneous genotyping sets of loci. Their variability was assessed in four populations. Four to 33 alleles were detected per locus; two to 23 alleles per population. Significant deviations from Hardy–Weinberg equilibrium could be attributed either to a mating system involving partial selfing or to null alleles. Genetic differentiation over all loci was significant among the four populations studied. These markers will constitute an efficient tool for investigating dispersal patterns in fragmented landscapes. Cross‐species amplification provided few loci variability in three other Crepis species (C. pulcra, C. foetida and C. rubra).     

Changes in axial hydraulic conductivity along elongating leaf blades in relation to xylem maturation in tall fescue

Xylem maturation in elongating leaf blades of tall fescue ( Festuca arundinacea ) was studied using staining and microcasting. Three distinctive regions were identified in the blade: (1) a basal region, in which elongation was occurring and protoxylem (PX) vessels were functioning throughout; (2) a maturation region, in which elongation had stopped and narrow (NMX) and large (LMX) metaxylem vessels were beginning to function; (3) a distal, mature region in which most of the longitudinal water movements occurred in the LMX. The axial hydraulic conductivity ( K _h) was measured in leaf sections from all these regions and compared with the theoretical axial hydraulic conductivity ( K _t) computed from the diameter of individual inner vessels. K _t was proportional to K _h throughout the leaf, but K _t was about three times K _h. The changes in K _h and K _t along the leaf reflected the different stages of xylem maturation. In the basal 60 mm region, K _h was about 0.30±0.07 mmol s⁻¹ mm MPa⁻¹. Beyond that region, K _h rapidly increased with metaxylem element maturation to a maximum value of 5.0±0.3 mmol s⁻¹ mm MPa⁻¹, 105 mm from the leaf base. It then decreased to 3.5±0.2 mmol s⁻¹ mm MPa⁻¹ near the leaf tip. The basal expanding region was observed to restrict longitudinal water movement. There was a close relationship between the water deposition rate in the elongation zone and the sum of the perimeters of PX vessels. The implications of this longitudinal vasculature on the partitioning of water between growth and transpiration is discussed.     

Measurement of a growth-induced water potential gradient in tall fescue leaves

Spatial distribution of cell turgor pressure, cell osmotic pressure and relative elemental growth rate were measured in growing tall fescue leaves ( Festuca arundinacea ). Cell turgor pressure (measured with a pressure probe) was c . 0.55 MPa in expanding cells but increased steeply (+0.3 MPa) in cells where elongation had stopped. However, cell osmotic pressure (measured with a picolitre osmometer) was almost constant at 0.85 MPa throughout the leaf. The water potential difference between the growth zone and the mature zone (0.3 MPa) was interpreted as a growth-induced water potential gradient. This and further implications for the mechanism of growth control are discussed.