Growth and differentiation of the testes in the large milkweed bug, Oncopeltus fasciatus (Dallas)

Abstract

During the fourth instar there is a five-fold increase i n testis volume, caused by mitotic proliferation of spermatogonia that leads to accumulation of many layers of cysts of resting spermatocytes. At the beginning of the fifth instar the basal cysts undergo meiotic division, and a wave of meiosis followed by spermateleosis progresses apically. There is little or no spermatogonial multiplication; the three-fold increase in testis size involves primarily spermatocyte differentiation. The wave of differentiation continues at a slower rate in the young adult; most of the spermatocyte cysts are transformed into about 250,000 spermatozoa by the twelfth day. Multinucleate apical cells that stain deeply with Feulgen reagent are present in the early fourth instar, enlarge i n the fifth, and persist in the adult testis.Spermatocyte differentiation is not affected by treatment of nymphs with a synthetic juvenile hormone analog during the fourth or fifth instar, although the treatment causes moderate to high juvenilization at the metamorphic molt. Since late fourth-instar testes transplanted into mature male or female adults also undergo extensive transformation of spermatocytes into spermatozoa, molting is not required for differentiation. Treatment of late fourth or early fifth instar nymphs with the chemosterilant tretamine causes high mortality at the metamorphic molt, but the wave of spermatocyte differentiation during the fifth instar proceeds normally, although there is evidence of severe chromosome damage.Comparisons with development in the female of Oncopeltus and in other insect species suggest that there is a profound change in the biochemical milieu at the molt from fourth to fifth instar, many processes preceding this molt tending to be larval in character and to diminish or disappear afterward while processes normally occurring after the molt tend to be adultoid.

A weapons–testes trade-off in males is amplified in female traits

“…Males of this size did not grow sizeable horns if ablation occurred earlier in development. In N. femorata hind limbs experience drastic growth in the final two moults, and this is same ontogenetic window where gonads develop across the Hemiptera [47,48]. We stimulated insects to drop a single hind leg prior to the final two moults, and the testes grew.…”

Adult nutrition, but not inbreeding, affects male primary sexual traits in the leaf‐footed cactus bug Narnia femorata (Hemiptera: Coreidae)

“…All juveniles in our study had access to the high‐quality diet until adult eclosion. This excellent nutrition may have come at the crucial time for the development of sperm traits, as spermatogenesis initiates during the penultimate and ultimate juvenile instars in other hemipterans (Economopoulos and Gordon ; Brent ). Even if adult nutrition negatively affected sperm traits, the males in our study could have generated a supply of mature sperm in their seminal vesicles that was not depleted, even as testes apparently shrank (our males were housed alone, without access to females).…”

“…). For hemimetabolous insects specifically, adult diet is predicted to have a significant effect on sperm traits and testis growth as spermatogenesis continues through adulthood (Economopoulos and Gordon ; Dumser and Davey ).…”

“…While testis development (reviewed in Martin et al 2012) and sperm traits (Rahman et al 2014) are especially influenced by juvenile diet (Gage and Cook 1994;McGraw et al 2007), the effects of adult diet on these traits remain unresolved (Hellriegel and Blanckenhorn 2002;Amitin and Pitnick 2007;Fricke et al 2008;Bunning et al 2015). For hemimetabolous insects specifically, adult diet is predicted to have a significant effect on sperm traits and testis growth as spermatogenesis continues through adulthood (Economopoulos and Gordon 1971;Dumser and Davey 1974).…”

Males that drop a sexually selected weapon grow larger testes

“…). We induced autotomy at the beginning of the fourth (penultimate) juvenile instar, since heteropteran testes undergo increased growth later in juvenile development (Economopolous and Gordon ; Dumser and Davey ). At this life stage, determining the sex of individuals is prohibitively difficult, thus we induced autotomy on individuals regardless of their sex.…”