Academic literature on the topic 'Hakea – Physiology'

To convert acoustic energy into estimates of fish density, the target strength (TS) of a representative fish must be known. TS is a measure of the acoustic reflectivity of a fish, which is variable depending on the presence of a swimbladder, the size of the fish, its behavior, morphology, and physiology. The most common method used to estimate the TS of a fish is a TS-to-length empirical regression, with TS values increasing with fish length. This study uses in situ and ex situ TS measurements and a backscatter model to develop TS-to-length conversions for Pacific hake (Merluccius productus). Results from in situ and ex situ measurements had regression intercepts 4–6 dB lower than the previous Pacific hake TS-to-length regression. These differences suggest that an individual hake reflects 2.5–4 times less acoustic energy than was previously estimated.

Effects of temperature on the spectral properties of visual pigments were measured in the physiological range (5–28°C) in photoreceptor cells of bullfrog (Rana catesbeiana) and crucian carp (Carassius carassius). Absorbance spectra recorded by microspectrophotometry (MSP) in single cells and sensitivity spectra recorded by electroretinography (ERG) across the isolated retina were combined to yield accurate composite spectra fromca. 400 nm to 800 nm. The four photoreceptor types selected for study allowed three comparisons illuminating the properties of pigments using the dehydroretinal (A2) chromophore: (1) the two members of an A1/A2 pigment pair with the same opsin (porphyropsinvs.rhodopsin in bullfrog “red” rods); (2) two A2 pigments with similar spectra (porphyropsin rods of bullfrog and crucian carp); and (3) two A2 pigments with different spectra (rodsvs.long-wavelength-sensitive (L-) cones of crucian carp). Qualitatively, the temperature effects on A2 pigments were similar to those described previously for the A1 pigment of toad “red” rods. Warming caused an increase in relative sensitivities at very long wavelengths but additionally a small shift of λmaxtoward shorter wavelengths. The former effect was used for estimating the minimum energy required for photoactivation (Ea) of the pigment. Bullfrog rod opsin with A2 chromophore hadEa= 44.2 ± 0.9 kcal/mol, significantly lower (one-tailedP< 0.05) than the valueEa= 46.5 ± 0.8 kcal/mol for the same opsin coupled to A1. The A2 rod pigment of crucian carp hadEa= 42.3 ± 0.6 kcal/mol, which is significantly higher (one-tailedP< 0.01) than that of the L-cones in the same retina (Ea= 38.3 ± 0.4 kcal/mol), whereas the difference compared with the bullfrog A2 rod pigment is not statistically significant (two-tailedP= 0.13). No strict connection between λmaxandEaappears to exist among A2 pigments any more than among A1 pigments. Still, the A1 → A2 chromophore substitution in bullfrog opsin causes three changes correlated as originally hypothesized by Barlow (1957): a red-shift of λmax, a decrease inEa, and an increase in thermal noise.

A detailed study of gametes development and characterization of plasma sex steroid hormones during the maturation cycle was performed for the first time in the southern hake (Merluccius australis). Fish were caught in the inland waters of the Reloncaví Sound, Interior Sea of Chiloé, Chile. Samples of gonads and blood were collected for histology and sex steroid hormone (17 β-estradiol, 11-ketotestosterone and 17,20 βdihydroxy-4-pregnen-3-one) analysis, respectively. Sex steroid hormone quantification was performed using enzyme-immunoassay (ELISA). Results showed that M. australis males and females have asynchronous development of testicles and ovaries, in all stages of maturation. Most spawning fish were found during the spring months. Regarding the sex steroid hormones, serological fluctuations of 17 β-estradiol and 11- ketotestosterone were found during gonadal maturation of M. australis. These hormones are the main hormones responsible for vitelogenesis and spermatogenesis processes, respectively. Conversely, 17,20 β-dihydroxy-4- pregnen-3-one did not show any serological fluctuation in females and males. Further studies involving gonadotropins, 17,20 β,21-trihydroxy-4-pregnen-3-one and vitellogenin quantification are required in order to obtain a more complete description of the reproductive physiology of wild and farmed M. australis.

[Truncated abstract] In south-western Australia a rare plant community occurs on shallow soils overlaying massive ironstone rock. These 'ironstone communities' are open shrublands, which are subject to extremes in drought and solar radiation and support many rare and endemic species. The restricted distribution of many of these species may be related to their high degree of specialisation to this harsh habitat and their inability to respond plastically to different environmental conditions. Indeed, earlier work has shown that ironstone Hakea species (Proteaceae) have a specialist root-system morphology investing mainly in deep roots, thereby increasing their chance of accessing cracks in the rock surface and obtaining water before the onset of summer drought. In this thesis I further examine aspects of specialisation and its possible consequences for species rarity using two ironstone Hakea species and comparing them with two of their widely distributed congeners. In the first experiment (Chapter 2) I explore inherent drought tolerance, independent of root-system morphology, as a further specialisation to the ironstone environment. All species were grown in sand in pots in a glasshouse for 7 months and then droughted for 5 weeks. There was no evidence that the ironstone species had a greater inherent drought tolerance than their common congeners. During drought all species maintained leaf water content of mature leaves by reducing stomatal conductance and osmotically adjusting, though ironstone species tended to OA (osmotic adjustment) more than common species. ... This suboptimal investment of resources may result in a lower competitive ability in shadier environments, and thus could partially explain their restricted distribution. In Chapter 4, I investigated the plasticity of root traits in response to levels of phosphorus supply. South-western Australian soils are phosphorus impoverished and phosphorus is well known to elicit plastic responses in root allocation and architecture. Ironstone species showed less plasticity in total root length, producing similar root length across P treatments, while common species showed an increase in root length with increasing [P]. Other root characteristics were similarly plastic in response to P treatment between species. However, when supplied with increasing [P], ironstone species invested an increasing proportion of roots in the bottom of pots while common species invested more in the top. This differential response in root allocation in response to P may reflect a fundamental trade-off between nutrient and water acquisition, with the ironstone species mainly foraging for water and investing in deeper roots, while the common species invest more in superficial roots to obtain nutrients. In conclusion, the rarity and restricted distribution of the ironstone Hakea species may be related to their specialist root-system morphology as well as a lowered phenotypic plasticity of functional traits. A reduction in plasticity may reduce their competitive ability outside their ironstone habitats, and thus contribute to the restricted distribution of these species. This may also be the case for other rock-outcrop endemics and more generally, for other rare plant species restricted to particular habitats where a lowered phenotypic plasticity in traits relevant to their particular habitat may contribute to their restricted distribution.