Winter mortality can be a strong selective pressure on animals living in temperate regions, especially for young and small individuals. Therefore, understanding the mechanism for its size-dependence ...is important to predict population dynamics of the species in a fluctuating environment. In this study, we experimentally investigated the effects of body size, temperature and energy reserve depletion on the overwinter mortality of young mudskipper fish (Boleophthalmus pectinirostris). Small size-class fish (<44 mm in SL) died earlier than large size-class fish (≥44 mm) under both heated and unheated temperature conditions. Relatively higher energy and lipid content in live compared to dead fish and suspended mortality during the warm period under unheated conditions suggested the effects of both energy depletion and low temperature on overwinter mortality. Small size-class fish showed a relatively higher energy depletion rate under both temperature conditions probably due to their higher mass-specific metabolic rate. Since small size-class fish died earlier than large size-class fish, the body size difference in energy depletion rate may be one of the factors affecting the size-dependence of overwinter mortality. The energy depletion rate gradually decreased with the progress of experiment, suggesting that fasting-induced metabolic depression occurred. The estimated relative lipid mass decreased with the progress of experiment. The lipid depletion rate with elapsed days significantly reduced in small size-class fish under unheated conditions comparing with large size-class fish, while the rate in large size-class fish was significantly larger than that of small size-class fish in heated conditions. The difference suggests the possibility that small size-class fish switches metabolic fuels at a relatively lower temperature condition to maintain a minimum activity level for unpredictable feeding opportunities during the pre-winter season.
•Small young mudskipper fish died earlier than large one during winter.•Early death of small fish may be caused by their higher energy depletion rate.•Fasting-induced metabolic depression may have occurred.•Lipid depletion rate was reversed between size classes depending on temperature.•Temperature-specific metabolic depression may improve survival of small fish.
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•Extensive sampling of estuarine gobies around the Australian coastline.•Multiple lines of evidence for at least six cryptic species.•Major unrealized biodiversity occurs in the ...region and potentially abroad.•Diverse estuarine faunas need consideration with future development and management.
Snubnose gobies (genus Pseudogobius: Gobionellinae) are ubiquitous to, and important components of, estuarine ecosystems of the Indo-west Pacific. These small benthic fishes occur in freshwater, brackish and marine habitats such as mangroves, sheltered tide pools and lowland streams, and represent a model group for understanding the biodiversity and biogeography of estuarine fauna. To develop the species-level framework required for a concurrent morphological taxonomic appraisal, we undertook thorough sampling around the extensive Australian coastline, referenced to international locations, as part of a molecular systematic review using both nuclear and mitochondrial markers. The results indicate that while there are currently eight recognised species, the true diversity is close to double this, with a hotspot of endemism located in Australia. Complicated patterns were observed in southern Australia owing to two differing zones of introgression/admixture. Key drivers of diversity in the group appear to include plate tectonics, latitude, and historic barriers under glacial maxima, where an interplay between ready dispersal and habitat specialisation has led to regional panmixia but frequent geographic compartmentalisation within past and present landscapes. The findings have significant implications for biodiversity conservation, coastal and estuarine development, the basic foundations of field ecology, and for applied use such as in biomonitoring.
A checklist of 73 gobiid species (Teleostei: Gobiidae) recorded to date from the Mediterranean Sea is established following the evidence approach for checklists. The Mediterranean gobiofauna ...currently has 62 known native species and 11 alien species. An identification key to gobiid species known from the area is provided. The principles of character selection for the key are discussed.
Parasites have deleterious effects on their hosts, often resulting in altered host behavior or increased energy expenditure. When organisms are exposed to suboptimal environments, parasite loading ...may increase. Microbialite pools along the warm temperate South African coastline have been hypothesized as refugia for Epaulette gobies (Coryogalops sordidus, Gobiidae) when they are outside of their previously known subtropical distribution. The aim of this study was to determine if C. sordidus individuals infected with metacercarial cysts display higher metabolic rates or different swimming behavior compared to noninfected individuals. We measured each goby's swimming performance using a critical station‐holding speed (Ucrit) test (n = 60) and visually scored their swimming behavior (n = 52) during these measurements. Also, we measured the metabolic rate of gobies using an intermittent flow respirometer system to determine standard metabolic rate (SMR) and maximum metabolic rate (MMR) from gobies at 21°C before and after swimming trials. Metacercarial load carried by infected gobies seemingly had no impact on the host's energetics (SMR or MMR), swimming ability (as repeated Ucrit tests), or swimming behavior compared to noninfected gobies. Thus, the metacercarial intensity observed in gobies in the current study appeared to have no impact on host swimming performance or behavior. Furthermore, the swimming capacity observed for C. sordidus, in general, suggests that this goby is a poor swimmer compared to other gobiid species.
Although longjaw mudsucker (Gillichthys mirabilis, Gobiidae) has been studied extensively for its ability to occupy low‐oxygen environments, few studies have addressed the evolution of its ...exceptionally elongated jaws that extend posteriorly beyond the gill opening in large adults. In this study, the ontogeny of the maxillae of G. mirabilis, Gillichthys seta, and the out‐group species Eucyclogobius newberryi was studied within the heterochrony framework using digitized landmarks and caliper measurements. The results show that the maxilla of both species of Gillichthys evolved via acceleration (increased growth rate) and that of G. mirabilis via hypermorphosis (continued growth to a larger body size); two forms of peramorphosis. This is in contrast to earlier studies that concluded that G. seta is paedomorphic. We were unable to confirm an earlier hypothesis of sexual dimorphism in the jaw length of G. mirabilis. The evolution of the elongated jaws and associated large buccopharyngeal membrane in G. mirabilis is hypothesized to increase the surface area for gas exchange during aerial respiration and may also serve to amplify the aggressive gaping display as observed in other fishes.
Invasive species have the potential to damage ecosystems outside their native range. At an invasion front, individuals are faced with the unfamiliar conditions of a novel environment. Therefore, ...certain behavioural traits such as boldness and movement likely play a role in invasion ecology. If behavioural traits of this kind are influenced by differing selection pressures between demographic groups of the same species, this could have broad implications for the management of expanding invasion fronts. To determine whether the invasive round goby (Neogobius melanostomus, Pallas, 1814) exhibits sex- and habitat-based differences in boldness and movement across the invasion front, the authors assessed individual movement and exploration tendency under controlled lab settings using video analysis in a behavioural assay. N. melanostomus from lakes tended to be bolder than those from streams, and females tended to be bolder than males. This study provides evidence for sex- and habitat-based differences in behaviour in this globally invasive species that the authors hope will assist in forming the foundation for contextually appropriate management strategies.
Biological invasions are frequently studied topics in ecological research. Unfortunately, within invasion ecology parasite-associated aspects such as parasite impacts on new environments and on local ...host populations are less well-studied. Round gobies migrating from the Ponto-Caspian region into the Rhine River system are heavily infested with the Ponto-Caspian acanthocephalan parasite Pomphorhynchus laevis. As shown by experimental infestations the acanthocephalans occur as pre-adults in host-encapsulated cysts within the internal organs of the migrating gobies, but remain infective for their definitive host chub. Recently, we described the occurrence of larvae of another parasite, the invasive eel swim bladder nematode Anguillicola crassus, in these Pomphorhynchus cysts. In the present study, we could prove the infectivity of the nematode larvae for European eels for the first time. After experimental inoculation of Pomphorhynchus cysts occasionally infested with A. crassus larvae, the nematodes grow to maturity and reproduce whereas all P. laevis were unviable. We therefore postulate that the nematode larvae behave like immunological hitchhikers that follow a "Trojan horse strategy" in order to avoid the paratenic host's immune response. Accordingly, the interaction between both invasive parasites gives first evidence that the invasional meltdown hypothesis may also apply to parasites.
Here, we combined archived mitochondrial sequences for Ponto-Caspian gobiids with new sequences from the south Caspian basin to assess and evaluate its gobioid diversity and taxonomy, and to provide ...a first mitochondrial-based phylogenetic and phylogeographic framework. We demonstrate that: (i)
Proterorhinus nasalis
is the tubenose goby taxon in the saline waters of the southern Caspian Sea, whereas the name
Pr. semipellucidus
for the Azov/northern Caspian Sea/Volga River populations is likely be resurrected depending on the outcome of an integrative taxonomical approach; (ii) the deep-water goby
Ponticola bathybius
should be re-assigned to the genus
Neogobius
, as it is the sistergroup of
N. melanostomus
; (iii) specimens previously identified as
Po. cyrius
and
Po. iljini
from the south Caspian basin appear conspecific with
Po. iranicus
and
Po. gorlap
, respectively, and should be omitted from the checklist of Iranian and south Caspian freshwater fishes; (iv) the low stand of the Caspian Sea during the Tyurkyanian regression is inferred to have led to the isolation and evolution of
Po. iranicus
; and (v) similarities in genetic background, and invasion history of
Rhinogobius
sp. and
Pseudorasbora parva
in Iran and Turkmenistan indicate that the initial introduction of both species into the region possibly originated from Japan in the 1980s.
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