Research Article |
Corresponding author: Josef Wanzenböck ( josef.wanzenboeck@uibk.ac.at ) Academic editor: Emili García-Berthou
© 2021 Josef Wanzenböck, Mathias Hopfinger, Sylvia Wanzenböck, Lukas Fuxjäger, Hans Rund, Dunja K. Lamatsch.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wanzenböck J, Hopfinger M, Wanzenböck S, Fuxjäger L, Rund H, Lamatsch DK (2021) First successful hybridization experiment between native European weatherfish (Misgurnus fossilis) and non-native Oriental weatherfish (M. anguillicaudatus) reveals no evidence for postzygotic barriers. NeoBiota 69: 29-50. https://doi.org/10.3897/neobiota.69.67708
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The European weatherfish Misgurnus fossilis (Linnaeus, 1758) is a threatened freshwater species in large parts of Europe and might come under pressure from currently establishing exotic weatherfish species. Additional threats might arise if those species hybridize which has been questioned in previous research. Regarding the hybridization of M. fossilis × M. anguillicaudatus (Cantor, 1842), we demonstrate that despite the considerable genetic distance between parental species, the estimated long divergence time and different ploidy levels do not represent a postzygotic barrier for hybridization of the European and Oriental weatherfish. The paternal species can be easily differentiated based on external pigment patterns with hybrids showing intermediate patterns. No difference in standard metabolic rate, indicating a lack of hybrid vigour, renders predictions of potential threats to the European weatherfish from hybridization with the Oriental weatherfish difficult. Therefore, the genetic and physiological basis of invasiveness via hybridization remains elusive in Misgurnus species and requires further research. The existence of prezygotic reproductive isolation mechanisms and the fertility of F1 hybrids remains to be tested to predict the potential threats of globally invasive Oriental weatherfish species.
Freshwater fish, genome size, pigment patterns, postzygotic barrier, standard metabolic rate
Freshwater fish biodiversity is declining at an alarming rate (
The European weatherfish is a native species distributed across Europe and western Asia and is of significant conservation concern (
A high probability of direct contact of the European and Oriental weatherfish in the same waterbody can be foreseen in the near future because of similar habitat preferences (
Therefore, we tested in a primarily qualitative study for 1) the presence/absence of postzygotic reproductive isolation measured as embryo/larval viability by conducting a reciprocal hybridization experiment, and 2) the presence/absence of heterosis effects manifested in a physiological trait such as standard metabolic rate in relation to genome size and/or ploidy levels.
Eight adult individuals of the European native species (European weatherfish, M. fossilis, see Suppl. material
Five adult fish of the non-native species M. anguillicaudatus, (see Suppl. material
Non-native fishes were held in a large (400 Liter), unheated aquarium over the autumn 2017 and winter 2017/2018. Eggs of two females (18 and 22 cm total length respectively) and sperm of 3 adult males were used for the experiments. The aquarium was in an unheated room and was exposed to natural temperature rise in spring 2018, and natural daylight from a large window in close proximity. Three weeks before hormone treatment was initiated (May 25), both aquaria inhabited by native and alien weatherfish respectively, were heated using aquarium heaters from 16 °C to 21 °C at a rate of 1 °C every other day.
Hormone treatment was performed following
The Standard Metabolic Rate (SMR) is defined as the minimal amount of oxygen needed to maintain the aerobic metabolism. There are eight different definitions on how to estimate the SMR (
Relative genome size was determined in 10 individuals of each group, following the protocol of
Larvae developed normally without any apparent morphological aberrations in all three groups (M. fossilis, M. anguillicaudatus, and hybrids produced from M. fossilis females and M. anguillicaudatus males). Different pigmentation patterns for these two parental species became apparent during the first weeks of development, with hybrids showing intermediate pigmentation (Figs
Pictures of weatherfishes taken one month after hatching (30.6.18) when larvae transformed into juveniles. Top panel: M. fossilis with larval fin fold still present. Center panel: Hybrid weatherfish with rests of larval fin fold present. Lower panel: M. anguillicaudatus – only small remnants of larval fin fold visible. Photographs: Sylvia Wanzenböck.
Pictures of weatherfishes taken two months after hatching (21.7.18) when development to juveniles was nearly completed. Top panel: M. fossilis with larval fin fold still visible. Center panel: Hybrid weatherfish without larval fin fold. Lower panel: M. anguillicaudatus – juvenile and no larval fin fold visible. Photographs: Sylvia Wanzenböck.
The lateral side of M. fossils can be separated into 4 distinguishable color bands. The overall dorsal part is dark brown. The first band is light yellowish colored and clearly separates from the dark brown band along the lateral line. Ventral to the brown lateral line band another light yellowish color band follows. A thin but distinct dark brown color band separates the ventral side (brown to yellow or sometimes a slightly red color) from the second light yellowish color band. In all dark color bands, several small dark spots might be present. The dorsal dark brown color line on the lateral side can be dispersed into a loose line of brown dots and may end just below the dorsal fin. The most ventral brown color band extends from the basis of the pectoral fins to the pelvic fins, and in some individuals to the basis of the anal fin. This band can be dispersed into a loose line or an interrupted row of brown dots.
Pictures of weatherfishes taken three months after hatching (26.8.18) when development to juveniles was completed. Top panel: M. fossilis. Center panel: Hybrid weatherfish. Lower panel: M. anguillicaudatus. Photographs: Lukas Fuxjäger.
Pictures of weatherfishes taken four months after hatching (1.10.18) showing advanced juvenile stages. Top panel: M. fossilis. Center panel: Hybrid weatherfish. Lower panel: M. anguillicaudatus. Photographs: Sylvia Wanzenböck.
The hybrids of M. fossils and M. anguillicaudatus show a brown-yellowish speckled overall pattern on the dorsal (and part of the lateral) side. The edge of this pattern often consists of a more or less continuous alignment of dark brown dots. It stretches from the eye to the base of the caudal peduncle. Often there is a loose and interrupted row of dots between the base of the dorsal fin and the caudal peduncle. The first color band is light yellowish and filled with several small dark brown dots. It stretches from the gill openings to the base of the caudal peduncle and contains various numbers of small brown dots, which increase in number with age. This color band is not as distinct as in M. fossilis. A dark brown color band along the lateral line from the gill openings to the base of the caudal peduncle forms the second color band. This one is also not as clearly distinct as in M. fossilis. The third light yellowish band, just next to the second one, is often filled with fine brown dots, and stretches from the base of the pectoralis to the base of the caudal peduncle. This more or less strongly dotted yellowish line is sometimes not clearly distinguishable from the fourth color band which is often dispersed into an interrupted and incomplete alignment of big brown dots. It extends from the basis of the pectoral fin to the ventral fin and in some individuals until the basis of the anal fin.
The basic coloration of M. anguillicaudatus varies from gray to sand-colored. On the dorsal and lateral side of the body more or less clearly visible dark dots are recognizable in an irregular pattern. Individuals with a high number of dark dots on the lateral side show a thin light band along the lateral line from the gill openings to the base of the caudal peduncle. Just before the dark bow on the very end of the caudal peduncle (sometimes divided, forming a dorsal and ventral black dot), a light half-moon shaped line is located. But there are also individuals without any dots. Pigmentation patterns were variable between individuals (Fig.
Pictures of weatherfishes taken four months after hatching (1.10.18) showing advanced juvenile stages and individual variation in pigmentation patterns. Left column: M. fossilis. Center column: Hybrid weatherfish. Right column: M. anguillicaudatus. Photographs: Sylvia Wanzenböck.
Standard metabolic rate (SMR) was found to depend negatively on fresh weight even when oxygen consumption values were calculated per unit weight (gram fresh weight – Fig.
Standard metabolic rate (measured as oxygen uptake per gram fresh weight per hour of juvenile M. fossilis (N = 8), juvenile hybrids (N = 7) and juvenile M. anguillicaudatus (N = 9) versus fresh weight (average of lowest 10% measurements over time ± SD). Note that N in this figure refers to number of chambers.
Average Standard metabolic rate (±SD) measured as oxygen uptake per gram fresh weight per hour for juvenile M. fossilis (N = 8), juvenile hybrids (N = 7) and juvenile M. anguillicaudatus (N = 9). Note that N in this figure refers to number of chambers.
Measurements of ploidy levels revealed relative genome sizes of 5.20 (±0.123) pg/nucleus, 4.77 (± 0.07), and 3.33 (±0.03) on average for M. fossilis, M. hybrids and M. anguillicaudatus, respectively (Fig.
Based on a genetic study using enzyme electrophoresis,
Differentiation between M. fossilis and various exotic weatherfish (in our case M. anguillicaudatus) was found to be easily possible based on pigmentation patterns (see also
Our estimates of SMR, measured as oxygen consumption (VO2), were comparable to previous estimates in a closely related loach species, i.e. the spined loach, Cobitis sp. (
We observed a negative trend in VO2 per gram wet mass with increasing body mass, which is a well – known pattern in the early ontogeny of larval and juvenile fish (
The relationship between metabolic rates and heterosis (or hybrid vigor, specifically in growth, i.e. “metabolic heterosis” sensu
Example of flow cytometer measurements. The first peak from the left is the internal standard (chicken red blood cells; similar in all measurements). The following peaks represent M. anguillicaudatus (green), hybrids (red), M. fossilis (purple).
Since representatives of the genus Misgurnus were found to show various ploidy levels (
Higher metabolic rates were found to correlate negatively with ploidy level in another loach species, i.e. spined loach, by
We showed that there is no postzygotic barrier for hybridization between the European and Oriental weatherfish despite the assumption given by
We are grateful to Julie Blommaert for English-language editing. The support of Sabine Wanzenböck during experiments and manuscript preparation is highly appreciated. Many thanks to Florian Glaser and Michael Schauer for providing material. Open access funding support was provided by the University of Innsbruck.
Figure S1
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Explanation note: Female Misgurnus fossilis used in the crossing experiment.
Figure S2
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Explanation note: Males of Misgurnus fossilis used in the crossing experiment.
Figure S3
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Explanation note: Female Misgurnus anguillicaudatus used in the crossing experiment.
Figure S4
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Explanation note: Male Misgurnus anguillicaudatus used in the crossing experiment.