Utilization patterns of estuarine and marine habitats by the halfbeak Zenarchopterus dunckeri at Iriomote Island,southern Japan,evaluated from otolith microchemistry

Estuarine and marine habitat use patterns in the halfbeak Zenarchopterus dunckeri were examined at Iriomote Island, southern Japan, by analyzing otolith Li/Ca and Sr/Ca ratios. The ranges of both Li/Ca and Sr/Ca ratios in juvenile Z. dunckeri from the maximum (30 psu) to minimum (0.5 psu) salinity levels of brackish water estimated from rearing experiments, were compared with those of wild individuals collected from upstream and downstream stations in the Urauchi River estuary. The majority of wild-caught individuals had invariable Li/Ca and Sr/Ca ratios along an otolith transect from the core to the posterior edge, which fell within the otolith Li/Ca and Sr/Ca ranges estimated for estuarine individuals in the rearing experiments, suggesting that such individuals developed within the estuary without migrating to a marine environment at any time, although some downstream-dwelling fish had higher otolith elemental ratios than the predetermined estuarine ranges in the mid transect section. The latter fish may have been accidentally flushed from the estuary into the sea by heavy flood events, subsequently returning to the estuary. The overall results suggested that Z. dunckeri is essentially an estuarine resident, completing its life cycle within an estuarine system.     

Exploring an East Asian melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) collection for parthenocarpic ability

In melon (Cucumis melo L.), the amount of fertile pollen decreases at low temperature during winter and early spring and thereby restricts fertilization. A promising way to overcome this problem is to develop parthenocarpic cultivars. Parthenocarpic cucumber and squash, but not melon cultivars are available. In this study, we explored 172 accessions from an East Asian melon collection and identified accessions that exhibited strong parthenocarpic ability throughout the year. Crosses between parthenocarpic accessions and a non-parthenocarpic cultivar, and among parthenocarpic accessions indicated that parthenocarpy may be inherited in a recessive manner and is likely controlled by the same gene or genes in these accessions. The parthenocarpic indices, such as the size and number of parthenocarpic fruits, differed among the cultivation periods, indicating the importance of environmental factors for parthenocarpic fruit development. We conclude that it is possible to breed new cultivars with stable parthenocarpic ability throughout the year by using the identified accessions.     

Strain analysis near the cutting edge in orthogonal cutting of hinoki (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>) using a digital image correlation method

A digital image correlation (DIC) method was utilized to measure strain distributed within approximately 0.5 mm of the cutting edge during slow-speed orthogonal cutting of air-dried hinoki (Chamaecyparis obtusa), to clarify the relationships of the strain distribution and cutting conditions, including cutting angle (\(\theta\)) and depth of cut (\(d\)). The strain was measured in 0.04 mm steps, and the measurable minimum strain was approximately 0.08%. Tensile strain of 3% or larger normal to the cutting direction, \({\varepsilon _y}\), tended to extend 0.2 mm or further ahead of the tool when \(\theta \leq 60^\circ\) and \(d \geq 0.1{\text{ mm}}\). This tensile \({\varepsilon _y}\) corresponded to the occurrence of the fore-split in Chip Type I. The tensile \({\varepsilon _y}\) detected along the path of the cutting edge decreased as \(\theta\) and/or \(d\) decreased. Positive shear strain, \({\gamma _{xy}}\), tended to be detected ahead of the tool in Type I. Negative \({\gamma _{xy}}\) tended to be detected ahead of the tool in Type II and III \(\left( {\theta \geq 70^\circ ,\,\,d \geq 0.05{\text{ mm}}} \right)\). These \({\gamma _{xy}}\) values were considered to be related to the elongation and shrinkage of the chip. The study confirmed the usability of the DIC method for the evaluation of cutting conditions and also to classify chip formation into chip types.     

Transmission of <Emphasis Type="Italic">Tomato chlorotic dwarf viroid</Emphasis> by bumblebees (<Emphasis Type="Italic">Bombus ignitus</Emphasis>) in tomato plants

Quantitative PCR revealed that Tomato chlorotic dwarf viroid (TCDVd) was present in substantial amounts in viroid-infected tomato flowers. Healthy tomato plants were arranged in two different glasshouses, and plants were mechanically inoculated with TCDVd. Bumblebees (Bombus ignitus) were then introduced into the glasshouses to reveal whether the viroid was transmitted from infected source plants to neighbouring healthy plants. TCDVd infection was found in neighbouring tomato plants more than 1 month after the introduction of the bees, some of which expressed symptoms, in both glasshouses. Thus, bumblebees transmitted TCDVd from tomato to tomato by pollination activities.     

Life in the fast lane: Revisiting the fast growth—High survival paradigm during the early life stages of fishes

Early life survival is critical to successful replenishment of fish populations, and hypotheses developed under the Growth-Survival Paradigm (GSP) have guided investigations of controlling processes. The GSP postulates that recruitment depends on growth and mortality rates during early life stages, as well as their duration, after which the mortality declines substantially. The GSP predicts a shift in the frequency distribution of growth histories with age towards faster growth rates relative to the initial population because slow-growing individuals are subject to high mortality (via starvation and predation). However, mortality data compiled from 387 cases published in 153 studies (1971–2022) showed that the GSP was only supported in 56% of cases. Selection against slow growth occurred in two-thirds of field studies, leaving a non-negligible fraction of cases showing either an absence of or inverse growth-selective survival, suggesting the growth-survival relationship is more complex than currently considered within the GSP framework. Stochastic simulations allowed us to assess the influence of key intrinsic and extrinsic factors on the characteristics of surviving larvae and identify knowledge gaps on the drivers of variability in growth-selective survival. We suggest caution when interpreting patterns of growth selection because changes in variance and autocorrelation of individual growth rates among cohorts can invalidate fundamental GSP assumptions. We argue that breakthroughs in recruitment research require a comprehensive, population-specific characterization of the role of predation and intrinsic factors in driving variability in the distribution and autocorrelation of larval growth rates, and of the life stage corresponding to the endpoint of pre-recruited life.     

The distribution and early growth of juvenile Pacific bluefin tuna Thunnus orientalis around Sado Island in the eastern Sea of Japan

Fisheries Science - The distribution and early growth of juvenile Pacific bluefin tuna (PBF) Thunnus orientalis were studied based on trawl surveys conducted around Sado Island, eastern Sea of...