Frequency of rearranged constituents for all chromosomal rearrangements in the <i>Simulium cholodkovskii</i> lineage, relative to the <i>Simulium</i> subgeneric standard.

<p>Frequency of rearranged constituents for all chromosomal rearrangements in the <i>Simulium cholodkovskii</i> lineage, relative to the <i>Simulium</i> subgeneric standard.</p

IIS arm of <i>Simulium cholodkovskii</i> (female larva), showing the typical sequence (<i>IIS-1</i>,4,<i>5</i>,<i>6</i>).

<p>Limits of polymorphic inversions IIS-7–IIS-9 and IIS-11 are indicated by brackets; <i>6</i>_<i>a</i> and <i>6</i>_<i>b</i> denote alternative breakpoints for <i>IIS-6</i>. The standard sequence for the subgenus <i>Simulium</i> can be obtained from the <i>IIS-1</i>,4,<i>5</i>,<i>6</i> sequence by alphabetically ordering the fragments indicated by small letters ‘a’ through ‘n’ that appear below the chromosome. Ordering the fragments above the chromosome from ‘a’ to ‘h’ produces the Y-chromosome sequence (<i>IIS-1</i>,<i>5</i>,<i>6</i>,10) of <i>S</i>. <i>nigricoxum</i>, i.e. IIS-10 is Y linked (dotted lines), whereas IIS-4 is X-linked (dashed lines) and, therefore, absent on the Y. Bu = bulge, C = centromere, Hb = location of heteroband 43Hb, RoB = ring of Balbiani, tr = trapezoidal.</p

IIIL arm of <i>Simulium decimatum</i>, showing continuity of transposed arms IS and IIIL and the <i>IIIL-2</i>,<i>15</i>,<i>23</i> sequence.

<p>The map represents a composite male (sections 98–100) and female larva, with sections 10–87 from the Thelon River and the remainder from the Tuul River. Polymorphic inversion IIIL-17, IIIL-19, and IIIL-25 (shared with <i>S</i>. <i>cholodkovskii</i>) are indicated by brackets. C = centromere, cs = cup and saucer marker, N.O. = nucleolar organizer.</p

IS arm of <i>Simulium cholodkovskii</i> (female larva), showing the <i>IS-17</i>,<i>18</i>,<i>19</i>,20,21 sequence.

<p>Fixed inversions <i>IS-17</i>,<i>18</i>,<i>19</i> are indicated with arrows below the chromosome, and predominant polymorphic inversions IS-20 and IS-21 with arrows above the chromosome; the basic <i>IS-17</i>,<i>18</i>,<i>19</i> sequence can be obtained from the <i>IS-17</i>,<i>18</i>,<i>19</i>,20,21 sequence by alphabetically ordering the fragments indicated by small letters ‘a’ through ‘h’. Limits of polymorphic inversions IS-22, IS-27, and IS-28 are indicated by brackets. C = centromere, em = end marker, gl = glazed, “3” = 3 marker;? = band unaccounted for but attributed to section 7.</p

Cytophylogeny of the <i>Simulium cholodkovskii</i> lineage, with terminals depicted by idiograms of each species.

<p>The outgroups (<i>S</i>. <i>erythrocephalum</i> and <i>S</i>. <i>vittatum</i>) are not shown on the cladogram. Rearrangements are shown in italics if fixed synapomorphies, in parentheses if polymorphic synapomorphies, and in square brackets if shared characters that could not be determined as plesiomorphic or synapomorphic. The homologues of each chromosome (I, II, III) are shown as tightly synapsed, and the arms are indicated as long (L) or short (S). Only diagnostic inversions (frequency > 0.10) for each species are shown on the idiograms. Fixed inversions are bracketed on the left. Polymorphic inversions are bracketed on the right as solid lines if autosomal, dashed if X-linked, and dotted if Y-linked. Landmarks are labeled on the idiogram for <i>S</i>. <i>cholodkovskii</i>: bl = blister with 2 heavy bands, Ce = centric region (with subscript indicating chromosome I, II, or III), em = end marker, Nk = neck, NO = nucleolar organizer, Pb = parabalbiani, RoB = ring of Balbiani.</p

IL arm of <i>Simulium nigricoxum</i> (female larva) from Canada, Thelon River, showing the <i>IL-1</i>,<i>17</i>,<i>18</i> sequence.

<p>The 3 fixed inversions are shown by a bracket (<i>IL-1</i>) and arrows (<i>IL-17</i>,<i>18</i>). The standard sequence for the subgenus <i>Simulium</i> can be obtained from the <i>IL-1</i>,<i>17</i>,<i>18</i> sequence by alphabetically ordering the fragments indicated by small letters ‘a’ through ‘l’. Limits of polymorphic inversions IL-19–IL-22 are indicated by brackets. C = centromere, Nk = neck.</p

Schematic derivation of the monocentric translocation homozygotes that define the <i>Simulium cholodkovskii</i> lineage.

<p>Diagnostic landmarks are given on idiograms for short (S) and long (L) arms of the three chromosomes (I, II, III). Both homologues of each chromosome are shown; bl = blister with 2 heavy bands, Ce = centric region containing putative centromere, em = end marker, Nk = neck, NO = nuclear organizer, Pb = parabalbiani, RoB = ring of Balbiani. Fixed inversions are italicized and bracketed on the left side of each chromosome; polymorphic inversions are in standard type and bracketed on the right side. A. Standard chromosomal complement, showing characteristic inversions of the <i>Simulium malyschevi</i> clade (<i>IL-1</i>, <i>IIL-1</i>, <i>IIL-2</i>, <i>IIIS-1</i>, and <i>IIIL-2</i>) from which the sequences of the <i>S</i>. <i>cholodkovskii</i> lineage are derived. From the ancestral intermediate through present-day members of the lineage (B–D), these inversions carry through as plesiomorphies, but are not shown in subsequent idiograms. B. Hypothetical intermediate of the <i>Simulium cholodkovskii</i> lineage, with characteristic fixed inversions established before the translocation event. Arrows 1 and 2 represent proximal and distal breaks, respectively, in the centric regions of chromosomes I and III. C. Derivation of a monocentric translocation heterozygote expressed as one of two possible scenarios: 1) As shown, chromosomal breaks occur in the proximal centric regions of chromosomes I and III (arrows 1 in Fig 10B) such that IS joins with CeIII plus IIIL and IL plus CeI joins with IIIS, giving rise to translocation heterozygote progeny (first generation). 2) (Not shown) chromosomal breaks occur in the distal centric regions of chromosomes I and III (arrows 2 in Fig 10B) such that IS plus CeI joins with IIIL and IL joins with CeIII plus IIIS. IIS is shown as the putative sex arm (X, Y). D. Monocentric translocation homozygote formed from an F1 mating. In our model, the first appearance of translocation homozygotes occurs in the F2 as a result of matings between F1 translocation males and females.</p

IS arm of <i>Simulium nigricoxum</i> (female larva) from Canada, Thelon River, showing the <i>IS-17</i>,<i>18</i>,<i>19</i> sequence.

<p>Breakpoints of fixed inversions are indicated by arrows. Limits of Y-linked IS-23, IS-24, IS-25, and IS-26 are indicated by dotted brackets. The standard sequence for the subgenus <i>Simulium</i> can be obtained from the <i>IS-17</i>,<i>18</i>,<i>19</i> sequence by alphabetically ordering fragments indicated by small letters ‘a’ through ‘j’. <i>IS-18</i> and <i>IS-19</i> share one coincident breakpoint. C = centromere, em = end marker, gl = glazed, “3” = 3 marker.</p

IIL arm of the <i>Simulium cholodkovskii</i> lineage.

<p>A. <i>Simulium decimatum</i> (female larva), showing the <i>IIL-1</i>,<i>2</i>,18 sequence. <i>IIL-1</i>,<i>2</i> are not bracketed but the renumbered sections (56–60) in the base of the arm indicate their presence. B. <i>Simulium cholodkovskii</i> (composite female + male larva [proximal 5 sections]), showing the IIL-16 sequence. C. <i>Simulium cholodkovskii</i> (female larva), showing the IIL-17 sequence. C = centromere, DNA = DNA puff, gB = gray band, Hb = location of heteroband 69Hb, Pb = parabalbiani, pf = puffing band, ‘3’ = 3 sharp.</p

Collections of larvae of the <i>Simulium cholodkovskii</i> lineage used in chromosomal analyses.

<p>Collections of larvae of the <i>Simulium cholodkovskii</i> lineage used in chromosomal analyses.</p