An article presenting a comprehensive analysis of the structural mechanics of dorsal vessel physiology in the mosquito, Anopheles gambiae, was published today in Journal of Experimental Biology.

The circulation of hemolymph (blood) by the insect open circulatory system is essential for the transport of nutrients, waste, signaling molecules, and immune factors throughout the hemocoel (body cavity). Hemolymph circulation is accomplished primarily via the pumping action of a muscular dorsal vessel that lies beneath the dorsal cuticle and runs the length of the body along the dorsal midline. The dorsal vessel is comprised of two distinct regions: the abdominal heart and the thoracic aorta.

Our earlier work revealed that the heart of adult mosquitoes contracts bidirectionally, propelling hemolymph toward the head (anterograde) and toward the posterior of the abdomen (retrograde) (See Glenn et al 2010 and Andereck et al 2010).  However, as holometabolous insects, mosquitoes undergo dramatic changes en route to adulthood.  That is, during their transition from an aquatic environment to a terrestrial habitat, mosquitoes undergo drastic metamorphic changes that are necessary for flight and reproduction, resulting in an adult body plan that differs significantly from that of larvae.

In this study we used intravital and fluorescence imaging techniques to visualize and quantify heart contraction dynamics and hemolymph flow velocity in Anopheles gambiae 4th instar larvae and adults.  Specifically we:

1. 1.Show that whereas the adult heart contracts in both anterograde and retrograde directions, the larval heart contracts exclusively in the anterograde direction.
   

2. 2.Show that the heart contraction rate and the velocity of hemolymph are slower in larvae when compared to adults.
   

3. 3.Present a comprehensive structural and functional comparison of the dorsal vessel in both life stages and highlight differences that may account for the markedly different hemolymph flow patterns observed between larval and adult mosquitoes.  These differences include the function of the posterior opening of the heart (incurrent in larvae but excurrent in adults) and the function of the abdominal ostia (inert in larvae but incurrent in adults).
   

In summary, this study provides an in-depth developmental comparison of the physiology of the dorsal vessel of mosquito larvae and adults.

Article citation:

League, G.P., O.C. Onuh and J.F. Hillyer. 2015. Comparative structural and functional analysis of the larval and adult dorsal vessel and its role in hemolymph circulation in the mosquito Anopheles gambiae. Journal of Experimental Biology. 218:370-80.

(PubMed) (See it in JEB) (Email me for a pdf copy)

Graphical abstract:

Article abstract:

Hemolymph circulation in insects is driven primarily by the contractile action of a dorsal vessel, which is divided into an abdominal heart and a thoracic aorta. As holometabolous insects, mosquitoes undergo striking morphological and physiological changes during metamorphosis. This study presents a comprehensive structural and functional analysis of the larval and adult dorsal vessel in the malaria mosquito Anopheles gambiae. Using intravital video imaging we show that, unlike the adult heart, the larval heart contracts exclusively in the anterograde direction and does not undergo heartbeat directional reversals. The larval heart contracts 24% slower than the adult heart, and hemolymph travels across the larval dorsal vessel at a velocity that is 68% slower than what is seen in adults. By fluorescently labeling muscle tissue we show that although the general structure of the heart and its ostia are similar across life stages, the heart-associated alary muscles are significantly less robust in larvae. Furthermore, unlike the adult ostia, which are the entry points for hemolymph into the heart, the larval ostia are almost entirely lacking in incurrent function. Instead, hemolymph enters the larval heart through incurrent openings located at the posterior terminus of the heart. These posterior openings are structurally similar across life stages, but in adults have an opposite, excurrent function. Finally, the larval aorta and heart differ significantly in the arrangement of their cardiomyocytes. In summary, this study provides an in-depth developmental comparison of the circulatory system of larval and adult mosquitoes.