INHERITANCE OF THE RED SNAKESKIN PATTERN AND COMPARATIVE GROWTH AMONG THREE DIFFERENT COLOUR STRAINS OF GUPPIES (POECILIA RETICULATA)

Abstract

The male guppy, Poecilia reticulata Peters 1859 exhibits remarkable polymorphism in the colour patterns of its body, dorsal and caudal fins. The gene responsible for this polymorphism are predominantly carried on the X- and Y -chromosomes. Over about 30 generations of artificial selection, close to 30 different and distinct strains of fancy guppies have been produced and maintained by local farmers.

To elucidate the gene control of the colour patterns of the Red Skaneskin (RSs) strain, single pair reciprocal crosses were set up between RSs and three other colour pattern strains -- Three-Quarter Black (3/4 B), Tuxedo (Tux) and Leopard Tail (LT).

Based on the results of inter-strain crosses and androgen treatment on P 1 and F I female fish, it was found that the Ssb and Sst snakeskin pattern genes are Y-linked and therefore only found on the male guppy, The Red tail (Rdt) gene is X-linked and sex-limited.

It is proposed that the expression of the X-linked Black tail (Bt) gene is affected by autosomal suppressor (sup) genes. When the sup genes are in the homozygous recessive state, the Bt gene is expressed phenotypically as black pigmentation in the tail but when the genes arc present in the heterozygous or homozygous dominant conditions, the yellow tail is expressed instead. In the presence of the Bt and dominant sup+ genes, the Rdt gene is not expressed as seen in the Fl progeny of RSs and 3/4 B crosses.

An interaction between the Bcp and Sst genes resulted in the snakeskin pattern on the tail to form black maculations instead of the fine vermiculations found in the RSs male.

The second study concerned the pleiotropic effects of colour genes on the growth performance of three different colour strains -- RSs, 3/4 B and Tux.

Under intra-strain competitive conditions, the weights of the three strains at 131 days after birth were not significantly different. However, under inter-strain competitive conditions between two different colour patterns, the RSs strain recorded poorer growth the the other two strains. This is attributed to the Ssb and Sst snakeskin pattern genes present in the male RSs strain guppy causing a reduction in its ability to compete with the 3/4 B and Tux strains. There were no significant differences in the mean weights of the 3/4 B and Tux strain guppies reared in competition with each other.

In all cases, the mean weights of the same strain reared under intra-strain competition were greater than those in inter-strain competition. The standard lengths were not significantly different amongst the three strains but the mean total length of the Tux strain male guppy was significantly less than those of the other two strain. This implies that the tail length of the Tux strain guppy is shorter.

Pleiotropic effects of the colour gene were al$0 extended to mortality. The 3/4 B strain guppy which exhibits black pigmentation on the tail had significantly higher mortality rates than the RSs and Tux strain guppies.