Hemoglobins of Kiefferulus, sister genus of Chironomus (Diptera: Insecta): Evolution of the Hb VIIB cluster

Abstract

A genomic clone containing hemoglobin genes was isolated from a species of the chironomid genus Kiefferulus. Eight genes, including an apparent pseudogene, were sequenced and the amino acid sequences of the putative proteins were determined. By comparison to the previously described hemoglobins in the sister-genus Chironomus, they were identified as members of the dimeric Hb VIIB group. The results indicate that the existence of clusters of hemoglobin genes may be a common feature in chironomids and not just confined to Chironomus. The Kiefferulus genes show greatest similarity of amino acid sequence to Hb VIIB-7 from the Chironomus cluster. The results suggest that the ancestral cluster contained at least two gene types, one of which gave rise to VIIB-7 and the Kiefferulus genes while the other gave rise to the other Chironomus VIIB genes. Both clusters appear to have increased in size by duplication or unequal crossing over since the separation of the genera. It also appears that an unrelated gene present in the Chironomus cluster, Hb-Y, arose from a completely independent origin with no apparent equivalent gene anywhere in the genome of Kiefferulus or some other Chironomus species.

Population variability in Chironomus (Camptochironomus) species (Diptera, Nematocera) with a Holarctic distribution: evidence of mitochondrial gene flow

“…In previous studies (e.g. Kao et al ., 1994; Chen et al ., 1995; Case et al ., 1997; Gruhl et al ., 1997; Guryev et al ., 2001) a separation time of 60 My for the separation of the globin genes of C. thummi and C. tentans has been used as the basis for calculating separation times of other species. This figure was derived from the Goodman et al .…”

Molecular Evolution of the Globin Gene Cluster E in Two Distantly Related Midges, Chironomus pallidivittatus and C. thummi thummi

“…Phylogenetic trees based on aa sequences of gb variants (Goodman et al 1983) and on nt sequences of the corresponding genes Trewitt et al 1995;Chen et al 1995) suggest that chironomid gb genes arose by successive steps of gene duplications and diversification. Unequal crossing over may have played a substantial role both in generating gene duplications and deletions.…”

“…In these calculations, CTT III and IV, with 18 aa differences in their mature protein, are supposed to have split about 40 Myr ago. This aa replacement rate, corrected for multiple substitutions (Kimura 1983), was used to infer the branching of C. t. thummi and the sibling species of C. pallidivittatus, C. tentans (Cte) at approximately 60 Myr ago (based on gb II␤ and gb IX distances; Kao et al 1994) and the splitting of Chironomus and its sister genus Kiefferulus at 50 Myr ago (based on gb VIIB distances; Chen et al 1995). Regarding the rather different, gene-specific substitution rates of the orthologous Cpa/Ctt cluster E gb genes, such simple calculations do not seem to be justified and may lead to erroneous conclusions.…”

“…The globin (gb) gene family of chironomid midges (Insecta, Diptera) is an attractive system for investigating the dynamics and evolutionary consequences of sequence redundancy. This multigene family consists of possibly more than 40 genes Rozynek et al 1989Rozynek et al , 1991Antoine et al 1987;Kao et al 1994Trewitt et al 1988Trewitt et al , 1995Chen et al 1995) which code for a multitude of gb protein variants of about 150 amino acids in length (Goodman et al 1983). At least some of these gb variants are known to be differentially expressed during development (Saffarini et al 1991).…”

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“…The amount of divergence between the sequences can be used to estimate the separation times of the populations. As in previous chironomid studies (Guryev et al 2001;Martin et al 2002), calibration of the molecular clock for Cytb sequences was performed using the time of the estimated split of the species Chironomus thummi and C. tentans (60 my), obtained using the substitution rate of invertebrate globin genes (Kao et al 1994) and comparison to slowly evolving Drosophila genes (Chen et al 1995). This converts to an mt sequence divergence rate of 0.75% (corrected distance) per my (Martin et al 2002).…”