Pond Boss Forums STOCKING A NEW POND Types of fish to choose RES Hybrids

There is a good bit of info from studies on RES Xs and BG Xs. This could take years to go over all the info on lepomis genetics/speciation. Below BR= BG X RES while RB= Recp cross RES X BG.


HYBRIDIZATION OF FISHES IN NORTH AMERICA
(FAMILY CENTRARCHIDAE)
by

W.F. CHILDERS



Sex Ratios of F1 hybrids
Sexually mature F1 hybrids were collected from each population and sexed. Of the 10 kinds of viable F1 hybrids, seven were predominately males (RB, BR, and BG were 97 percent males; WG were 84 percent males; and RG, GB, and BW were approximately 70 percent males), two were approximately 50 percent males (GR and RW), and one was predominately female (GW was 16 percent males). Ricker (1948) determined the sex of 428 BR F1 hybrids in Indiana and found them to be 97.7 percent males.

Sex determination in sunfishes is very poorly understood. Bluegills, green sunfish, and their F1 hybrids apparently have 24 pairs of chromosomes, and the sex chromosomes are indistinguishable from the autosomes (Bright 1937). Bright also reported that the chromosomes are so similar in shape and size that he was unable to detect specific differences. Roberts (1964) found that red-ear, bluegill, and warmouth sunfishes each have 24 pairs of chromosomes; green sunfish from North Carolina had 24 pairs; but green sunfish from West Virginia had only 23 pairs.

The unbalanced phenotypic tertiary sex ratios of the F1 hybrid sunfish could result from unbalanced primary genetic sex ratios, specific differences in the strength of sex-determining factors, an overriding of the genetic sex by environmental factors, or differential mortality of the sexes.

Since the WG F1 hybrids were 84 percent males and the reciprocal cross hybrids were 16 percent males, it is possible that the strength of sex-determining factors of warmouths are 5.25 times more powerful than those of green sunfish. Specific differences in the strength of sex-determining factors cannot alone explain the sex ratios of the remaining eight kinds of viable hybrids, since none of these were predominately females.

RB and BG F1 hybrids were both 97 percent males. If differential mortality were the cause of these unbalanced sex ratios, much of the mortality would have had to occur after the swim-up fry stages, since in the stripping experiments total mortality between fertilization and the swim-up fry stages was only 14 percent for the RB and 27 percent for the BG F1 hybrids.

It is not known which sex is the heterogametic condition for the sex chromosomes of the four experimental species; however, Haldane (1922) formulated a rule which furnishes a clue: “When in the F1 offspring of a cross between two animal species or races, one sex is absent, rare, or sterile, that sex is always the heterozygous sex.” Using Haldane's rule, Krumholz (1950), in a study concerning BR F1 hybrids, pointed out that the males of both bluegills and red-ear sunfish are probably homozygametic for sex and the females heterozygametic. The application of Haldane's rule to all possible F1 hybrids produced from red-ear sunfish, bluegills, and green sunfish indicates that the female is the heterozygametic sex in these three species. Hybridization of male warmouths with females of the three Lepomis species resulted in partial or complete lethals, suggesting that in the warmouth the male is the heterogametic sex.

4.2 Reproductive success of hybrids
The reproductive success of each of the 10 kinds of viable F1 hybrids was investigated in one or more ponds. The occurrence and abundance of F2 hybrids were determined by seining, trapping, shocking, poisoning or draining the ponds after the F1 hybrids were one or more years of age. RB, BR, and BG failed to produce abundant F2 generations when in ponds which contained no other species of fishes. In contrast to these results, BR F1 hybrids produced abundant F2 generations in two ponds in Indiana (Ricker 1948). The other seven kinds of F1 hybrids produced abundant F2 populations when stocked in ponds containing no other fishes. Three of the seven kinds of F1 hybrids which produced large F2 populations when stocked in ponds containing no other fishes were also stocked in ponds with largemouth bass. RG F1 hybrids and GB F1 hybrids, when stocked with largemouth bass, produced only a few F2 hybrids. No F2 hybrids were found in the pond stocked with BW F1 hybrids and largemouth bass. WG F2 hybrids and GW F2 hybrids were stocked in ponds containing no other fishes. Both of these F2 hybrids produced large F3 populations.

Backcrosses, outcrosses, a four-species cross, and a three-species cross involving F1 hybrids are listed in Table III. The BW × B backcross was made by stocking adult male BW F1 hybrids and adult female bluegills in a pond which contained no other fishes. The other 12 crosses listed in Table III were made by stripping gametes from ripe adults and rearing the young to the free-swimming fry stage in the laboratory.

R × RW, W × RW, B × RW, G × RW, R × GB, and RB × W young were killed after they developed into free-swimming fry because of the lack of ponds in which they could be stocked. All six kinds of fry appeared to be normal and probably would have developed into adults. Free-swimming fry of the remaining six crosses in the laboratory were stocked in ponds and did develop into adult fishes. BW × B, G × GW, and B × RG populations produced large numbers of young.Sex Ratios of F1 hybrids

Sexually mature F1 hybrids were collected from each population and sexed. Of the 10 kinds of viable F1 hybrids, seven were predominately males (RB, BR, and BG were 97 percent males; WG were 84 percent males; and RG, GB, and BW were approximately 70 percent males), two were approximately 50 percent males (GR and RW), and one was predominately female (GW was 16 percent males). Ricker (1948) determined the sex of 428 BR F1 hybrids in Indiana and found them to be 97.7 percent males.

Sex determination in sunfishes is very poorly understood. Bluegills, green sunfish, and their F1 hybrids apparently have 24 pairs of chromosomes, and the sex chromosomes are indistinguishable from the autosomes (Bright 1937). Bright also reported that the chromosomes are so similar in shape and size that he was unable to detect specific differences. Roberts (1964) found that red-ear, bluegill, and warmouth sunfishes each have 24 pairs of chromosomes; green sunfish from North Carolina had 24 pairs; but green sunfish from West Virginia had only 23 pairs.

The unbalanced phenotypic tertiary sex ratios of the F1 hybrid sunfish could result from unbalanced primary genetic sex ratios, specific differences in the strength of sex-determining factors, an overriding of the genetic sex by environmental factors, or differential mortality of the sexes.

Since the WG F1 hybrids were 84 percent males and the reciprocal cross hybrids were 16 percent males, it is possible that the strength of sex-determining factors of warmouths are 5.25 times more powerful than those of green sunfish. Specific differences in the strength of sex-determining factors cannot alone explain the sex ratios of the remaining eight kinds of viable hybrids, since none of these were predominately females.

RB and BG F1 hybrids were both 97 percent males. If differential mortality were the cause of these unbalanced sex ratios, much of the mortality would have had to occur after the swim-up fry stages, since in the stripping experiments total mortality between fertilization and the swim-up fry stages was only 14 percent for the RB and 27 percent for the BG F1 hybrids.

It is not known which sex is the heterogametic condition for the sex chromosomes of the four experimental species; however, Haldane (1922) formulated a rule which furnishes a clue: “When in the F1 offspring of a cross between two animal species or races, one sex is absent, rare, or sterile, that sex is always the heterozygous sex.” Using Haldane's rule, Krumholz (1950), in a study concerning BR F1 hybrids, pointed out that the males of both bluegills and red-ear sunfish are probably homozygametic for sex and the females heterozygametic. The application of Haldane's rule to all possible F1 hybrids produced from red-ear sunfish, bluegills, and green sunfish indicates that the female is the heterozygametic sex in these three species. Hybridization of male warmouths with females of the three Lepomis species resulted in partial or complete lethals, suggesting that in the warmouth the male is the heterogametic sex.

4.2 Reproductive success of hybrids
The reproductive success of each of the 10 kinds of viable F1 hybrids was investigated in one or more ponds. The occurrence and abundance of F2 hybrids were determined by seining, trapping, shocking, poisoning or draining the ponds after the F1 hybrids were one or more years of age. RB, BR, and BG failed to produce abundant F2 generations when in ponds which contained no other species of fishes. In contrast to these results, BR F1 hybrids produced abundant F2 generations in two ponds in Indiana (Ricker 1948). The other seven kinds of F1 hybrids produced abundant F2 populations when stocked in ponds containing no other fishes. Three of the seven kinds of F1 hybrids which produced large F2 populations when stocked in ponds containing no other fishes were also stocked in ponds with largemouth bass. RG F1 hybrids and GB F1 hybrids, when stocked with largemouth bass, produced only a few F2 hybrids. No F2 hybrids were found in the pond stocked with BW F1 hybrids and largemouth bass. WG F2 hybrids and GW F2 hybrids were stocked in ponds containing no other fishes. Both of these F2 hybrids produced large F3 populations.

Backcrosses, outcrosses, a four-species cross, and a three-species cross involving F1 hybrids are listed in Table III. The BW × B backcross was made by stocking adult male BW F1 hybrids and adult female bluegills in a pond which contained no other fishes. The other 12 crosses listed in Table III were made by stripping gametes from ripe adults and rearing the young to the free-swimming fry stage in the laboratory.

R × RW, W × RW, B × RW, G × RW, R × GB, and RB × W young were killed after they developed into free-swimming fry because of the lack of ponds in which they could be stocked. All six kinds of fry appeared to be normal and probably would have developed into adults. Free-swimming fry of the remaining six crosses in the laboratory were stocked in ponds and did develop into adult fishes. BW × B, G × GW, and B × RG populations produced large numbers of young.