Ontogenetic change in the amount and position of slow-oxidative myotomal muscle in relationship to regional endothermy in juvenile yellowfin tuna Thunnus albacares

Myotomal slow-oxidative muscle (SM) powers continuous swimming and generates heat needed to maintain elevated locomotor muscle temperatures (regional endothermy) in tunas. This study describes how the amount and distribution of myotomal SM increases with fish size and age in juvenile yellowfin tuna Thunnus albacares in relationship to the development of regional endothermy. In T. albacares juveniles 40–74 mm fork length (L_F; n = 23) raised from fertilised eggs at the Inter-American Tropical Tuna Commission Achotines Laboratory in Panama and larger juveniles (118–344 mm L_F; n = 5) collected by hook and line off of Oahu, Hawaii, USA, SM was identified by histochemical staining for the mitochondrial enzyme succinic dehydrogenase or by colour (in the two largest individuals). The cross-sectional area of myotomal SM at 60% L_F, a position with maximal percentage of SM in larger T. albacares, increased exponentially with L_F. The percentage of total cross-sectional area composed of SM at 60% L_F increased significantly with both L_F and age, suggesting that SM growth occurs throughout the size range of T. albacares juveniles studied. In addition, the percentage of SM at 60% L_F that is medial increased asymptotically with L_F. The increases in amount of SM and medial SM, along with the development of the counter-current heat-exchanger blood vessels that retain heat, allow larger tuna juveniles to maintain elevated and relatively stable SM temperatures, facilitating range expansion into cooler waters.     

Coloured LED light as a potential behavioural guidance tool for age 0 and 2 year walleye Sander vitreus

Based on existing laboratory research on the visual physiology of walleye Sander vitreus, we tested colours of known spectral sensitivity (i.e., green and orange) using constant and strobing (5 Hz) illumination with an LED-based light guidance device (LGD). Hatchery-reared age 0 and 2 years S. vitreus were exposed to these four light combinations as well as an unilluminated control treatment during day and night trials. Age 2 years S. vitreus generally avoided the LGD when light was produced (negative phototaxis) compared with the control, with continuous illumination having a greater effect than strobing. The proportions of both age 0 and 2 year fish exiting illuminating zones of the trial arena did not differ with light colour or strobe rate, suggesting that phototactic behaviours in S. vitreus do not change with ontogeny in these age classes. Our findings confirm that typical behavioural responses of S. vitreus to light stimuli are characterised by avoidance and provide evidence that the use of light for behavioural guidance (deterrence) may be effective at reducing entrainment and impingement of this species on hydraulic barriers during migrations, independent of ontogenetic stage.     

High air humidity is sufficient for successful egg incubation and early post‐embryonic development in the marbled crayfish (Procambarus virginalis)

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Ontogeny of locomotion in rhesus macaques (Macaca mulatta): II. Postural and locomotor behavior and habitat use in a free-ranging colony

This study quantifies changes in postural and locomotor behavior as well as habitat use across the life span of free-ranging rhesus macaques (Macaca mulatta) in the Cayo Santiago colony in Puerto Rico. It focuses on developmentally related changes from birth to adulthood, and complements an earlier study by Turnquist and Wells ([1994] J Hum Evol 26:487-499) on the early postnatal ontogeny of the musculoskeletal system of the same colony. A total of 6,551 locomotor and postural events was analyzed. Selection and use of substrate correlated well with age. The more sedentary adult and dependent infant select safe, wide, horizontal arboreal settings in contrast to the older Infant IIs and Juveniles, who are learning locomotor and postural skills through independent chase and play. Infant macaques, when independent, often employ a low center of gravity and widely abducted limbs in order to broaden their contact with the base of support. This study shows that the previously reported ontogenetic changes in morphology are closely paralleled by changes in postural and locomotor behavior, and these in turn are correlated to changes in habitat use, particularly during the formative years.     

Effect of Rhizobium Sp. Inoculation on N2-Fixing and Photosynthetic Activities of Two Cowpea [Vigna unguiculata (L.) Walp.] Genotypes

Time course of symbiotic N₂-fixing and photosynthetic activities during vegetative growth from 30 d after plantation until pod set was measured in the CB5 and 7964 cowpea [Vigna unguiculata (L.) Walp.] genotypes of contrasting senescence traits. At emergence, seedlings were inoculated with a "non-cowpea miscellany" Rhizobium strain generally used to inoculate Cicer arietinum. Maximum N₂-fixing activity occurred in inoculated CB5 and 7964 plants about 54 and 68 d after plantation, respectively. A similar temporal shift of maximum was found for net photosynthetic rate (P _N), confirming a good coordination between the two processes. A higher P _N was found from the first measurements in inoculated plants of both genotypes as compared with uninoculated plants. Apparently, the maximum activity of both N₂-fixation and P _N was timed to occur at a particular stage of plant ontogeny correlating the high N supply with the high N demand by the plant. Rhizobium inoculation did not significantly affect partitioning coefficients of biomass to various plant organs but extended leaf longevity by about 10 d in the CB5 genotype, retarding thus the monocarpic senescence. This revised version was published online in June 2006 with corrections to the Cover Date.     

Alternative Ways to Become a Juvenile or a Definitive Phenotype (and on Some Persisting Linguistic Offenses)

Lack of knowledge of early and juvenile development often makes it difficult to decide when a fish becomes a juvenile or, for that matter, a definitive phenotype. According to the established life-history model, a fish develops naturally in a saltatory manner, its entire life consisting of a sequence of stabilized self-organizing steps, separated by distinct less stabilized thresholds. Changes are usually introduced during thresholds. In principle, there are two ways to reach the juvenile period: by indirect or by direct development. Indirectly developing fishes have a distinct larva period that ends in a cataclysmic or mild remodeling process, called metamorphosis, from which the fishes emerge as juveniles. During metamorphosis, most temporary organs and structures of the embryos and larvae are replaced by definitive organs and structures that are also possessed by the adults. In contrast, directly developing fishes have no larvae. Their embryos develop directly into juveniles and do not need major remodeling. Consequently, the beginning of their juvenile period is morphologically and functionally less distinct than in indirect development. The life-history model helps to find criteria that identify the natural boundaries between the different periods in the life of a fish, among them, the beginning of the juvenile period. Looking at it from a different angle, when ontogeny progresses from small eggs with little yolk, larvae are required as the necessary providers of additional nutrients (feeding entities similar to amphibian tadpoles or butterfly caterpillars) in order to accumulate materials for the metamorphosis into the definitive phenotypes. Directly developing fishes start with large demersal eggs provided with an adequate volume of high density yolk and so require no or little external nutrients to develop into the definitive phenotype. These large eggs are released and develop in concentrated clutches. It therefore becomes possible and highly effective to guard them in nests or bear them in external pouches, gill chambers or the buccal cavity. Viviparity is the next natural step. Now the maternal investment into large yolks can be supplemented or replaced by direct food supply to the developing embryos like, for example, the secretion of uterine histotrophe or nutrient transfer via placental analogues. When the young of guarders and bearers start exogenous feeding, they are much larger or better developed than larvae of nonguarders and the larva period in the former is reduced to a vestige or eliminated entirely. In the latter case, the juvenile period begins with the first exogenous feeding. Such precocial fishes are more specialized and able to survive better in competitive environments. In contrast, altricial forms retain or revert to a life-history style with indirect development and high fecundity when dispersal is advantageous or essential. Fishes become juveniles when the definitive phenotype is formed in most structures, either indirectly from a larva via metamorphosis or directly from the embryo.     

Recovery of leaf area through accelerated shoot ontogeny in thrips-damaged cotton seedlings

BACKGROUND AND AIMS: Leaf area of cotton seedlings (Gossypium hirsutum) can be reduced by as much as 50 % by early season thrips infestations, but it is well documented that plants can regain the difference in leaf area once infestation ceases. The processes involved in the recovery have not been identified. Hypotheses include enhancement of the photosynthetic rate of the damaged leaves, more efficient leaf construction (i.e. more leaf area per unit of dry matter invested in new leaves), and more branching. METHODS: This 2-year field study examined these hypotheses and found that thrips-affected plants recovered from a 30 % reduction in total leaf area. During the recovery period, repeated measurements of gas exchange, leaf morphology and individual leaf areas at all nodes were made to assess their contribution to the recovery. KEY RESULTS: Recovery was not achieved through the previously proposed mechanisms. The pattern of nodal development indicated that the duration of leaf expansion of the smaller deformed leaves was shorter than that of control leaves, possibly because they had fewer cells. The production and expansion of healthy upper node leaves in thrips-affected plants could, therefore, begin sooner, about 1-2.5 nodes in advance of control plants. The proposed process of recovery was evident but weaker in the second year where thrips numbers were higher. CONCLUSIONS: It is concluded that thrips-affected plants overcame the leaf area disparity through an accelerated ontogeny of main stem leaves. By completing the expansion of smaller but normally functioning lower node leaves earlier, resources were made available to the unfolding of larger upper node leaves in advance of control plants. The generality of this mode of plant resistance in pest damage remains to be determined.     

Spore ontogeny of the arbuscular mycorrhizal fungus<Emphasis Type="Italic"> Archaeospora trappei</Emphasis> (Ames &; Linderman) Morton &; Redecker (<Emphasis Type="Italic">Archaeosporaceae</Emphasis>)

Arbuscular mycorrhizal (AM) fungi in the genus Archaeospora (family Archaeosporaceae) contain both monomorphic and dimorphic species. The synanamorphism is often hard to discern without ontogenetic observations. Here, the spore ontogeny of Ar. trappei is reported from single species pot culture studies. The sporogenous hypha swelled up to a terminal sporiferous saccule and produced a lateral spore primordium on its neck. The saccule expanded fully before the spore primordium emerged. The saccule transferred its contents into the expanding spore and collapsed while wall differentiation continued inside the spore. The spore wall of Ar. trappei differentiated sequentially, in discrete steps, as in Acaulosporaceae members. In contrast, Ar. trappei produced a simplified spore wall in which the components differed in chemical and physical characteristics from those of the Acaulosporaceae members. Ontogenetic studies confirmed Ar. trappei to be monomorphic and producing acaulosporoid spores. The fungus is a new record to New Zealand.     

Ontogeny of tracheal system structure: a light and electron-microscopy study of the metathoracic femur of the American locust, Schistocerca americana

Does oxygen delivery become more challenging for insects as they increase in size? To partially test this hypothesis, we used quantitative light and electron microscopy to estimate the oxygen delivery capacity for two steps of tracheal oxygen delivery within the metathoracic femur (jumping leg) for 2nd instar (about 47 mg) and adult (about 1.7 g) locusts, Schistocerca americana. The fractional cross‐sectional areas of the major tracheae running longitudinally along the leg were similar in adults and 2nd instars; however, since the legs of adults are longer, the mass‐specific diffusive conductances of these tracheae were 4‐fold greater in 2nd instars. Diffusive gas exchange longitudinally along the leg is easily possible for 2nd instars but not adults, who have many air sacs within the femur. Mitochondrial content fell proximally to distally within the femur in 2nd instars but not adults, supporting the hypothesis that diffusion was more important for the former. Lateral diffusing capacities of the tracheal walls were 12‐fold greater in adults than 2nd instars. This was primarily due to differences in the smallest tracheal class (tracheoles), which had thinner epidermal and cuticular layers, greater surface to volume ratios, and greater mass‐specific surface areas in adults. Adults also had greater mitochondrial contents, larger cell sizes and more intracellular tracheae. Thus, larger insects do not necessarily face greater problems with oxygen delivery; adult grasshoppers have superior oxygen delivery systems and greater mass‐specific aerobic capacities in their legs than smaller/younger insects. J. Morphol. 262:800–812, 2004. © 2004 Wiley‐Liss, Inc.     

The structure and development of haustorial placentas in leptosporangiate ferns provide a clear-cut distinction between euphyllophytes and lycophytes

This light and electron microscope study revealed that leptosporangiate ferns have highly distinctive gametophyte-sporophyte junctions characterized by sporophytic haustoria, the absence of intraplacental spaces and degenerating cells, and the early appearance of wall ingrowths in both generations. Other notable cytological features are highly pleomorphic plastids and mitochondrial aggregates in the gametophytic placental cells. Close similarities with the gametophyte-sporophyte junctions in Tmesipteris and major differences from those of homosporous lycophytes are in line with the placement of psilophytes and ferns in the same clade and distance both from lycophytes. A smooth interface between the two generations in Azolla suggests a clear-cut discontinuity between homosporous and heterosporous ferns, although this is the only heterosporous fern investigated to date. Similarities between the gametophyte-sporophyte junctions of leptosporangiate ferns and hornworts, when balanced against differences between them, are considered more likely the result of parallel evolution rather than homology.