Revision- Migration of Monarch Butterflies

Running head: MIGRATION OF MONARCH BUTTERFLIES 1

MIGRATION OF MONARCH BUTTERFLIES

Migration of Monarch Butterflies

Name

Institution

The monarch butterfly, as known as Danaus plexippus, is often called the milkweed butterfly because its larvae eat the milkweed plant. They are also sometimes called "royalty butterflies" because their family name comes from the daughter of Danaus, ruler of Argos. There are many other interesting facts about this butterfly including its anatomy and life cycle, where the butterfly lies on the food chain, the migration from Canada to Mexico, why the butterfly is being threatened, and lastly, what is being done to help the butterfly.      The anatomy of the monarch starts with it coloring. The monarch butterfly is bright orange with a white spots in a black margin around the edges. The veins on the wings are also black. The caterpillar is ringed with yellow, black, and white on each segment and has a pair of black fleshy tubercles at each end (Emmel, 1999). Monarchs smell with their antennae while they taste with their feet (Wexler, 1994). While the male monarchs have scent scales on their wings and "hair pencils" on their abdomens which secrete a scent (Emmel, 1999). The male scent is used during mating. The copulation of a male and female monarch can last from thirty to sixty minutes which is about average for most butterflies (Emmel, 1999).      The life cycle starts as larva or caterpillar. First, the monarch lays the eggs on the milkweed plants. Next, the egg hatch into a caterpillar. The caterpillar then eats the milkweed plants until they are large enough to pupate (Emmel, 1999). Then, the caterpillar attaches a pad of silk to a stem of a milkweed plant so it can hang while it transform into a butterfly. Next, the caterpillar sheds it larval skin to reveal the chrysalis inside (Emmel, 1999). After it shed its skin, the pupa hardens and the chrysalis earns it name by glowing in the sun. As the pupa stage comes to an end, the butterfly can be seen through its pupa shell. The monarch emerges by splitting the pupa along the length of it proboscis (Emmel, 1999). First the legs emerge. Then the fluid fill body pumps its fluid into the veins of the wings while the body shrinks to normal size. Finally, the butterfly hangs from the pupa about two hours while the wings dry (Emmel, 1999).

In eastern North America, monarch butterflies (Danaus plexippus) undertake a remarkable migration every fall, traveling up to3600 km to reach their overwintering groundsin central Mexico (1). Migrating monarchs use a time-compensated Sun compass to navigate

(2, 3). It is not known, however, how the circadian clock interacts with the Sun compass, which enables migrants to maintain southwesterly flight bearing as the Sun moves across the sky each day. To investigate the role of the circadianclock in monarch navigation, we first evaluated

the basic properties of the monarch circadian system by examining the time of day of adult emergence (eclosion) from the chrysalis(4), because eclosion is a reliable marker

of circadian function in other insects (5).Under laboratory light: dark conditions, adult

monarch eclosion was restricted to the early portion of the light period (Fig. 1A, upper

panel), as expected from field observations(6). A 6-hour shift of the light: dark cycle during adult development caused a corresponding shift in the average timing of eclosion (7). The eclosion rhythm persisted inconstant darkness, with adults emerging at the correct times as though they had remained in a light: dark cycle (Fig. 1A, middle panel).

These results indicate that the monarch eclosion rhythm is controlled by a light-entrained circadian clock. Constant light disrupted the timing of eclosion (Fig. 1A, lower panel), as occurs in other insects (8, 9), demonstrating that constant light provides a means of disrupting the monarch clock. To monitor the molecular clock after eclosion, we cloned the monarch period (per) cDNA (GenBank accession no. AY237279) (4), because per is an essential component of the circadian clock of Drosophila (8), and per RNA levels oscillate in flies and silkmoths(8, 9). Real-time polymerase chain reactions (PCRs) of per RNA levels from the heads of the recently emerged monarchs in the eclosion study were examined 24 hours later in the three lighting conditions (4). A robust rhythm in per RNA levels was detected under the light:dark condition, with high levels during the night and low levels during the day (P _ 0.01, one-way analysis of variance) (Fig. 1B). The rhythm persisted in constant darkness (P _ 0.01), with some dampening in amplitude and an apparent advance in timing (Fig. 1B). In the constant light group, the per rhythm was severely blunted (Fig. 1B), with RNA levels at constant low daytime values (P _ 0.05). Constant light thus disrupts the underlying clockwork mechanism, leading to the disruption of output rhythms (such as the timing of adult eclosion).To study the role of the circadian clock in migratory flight behavior, we used the Mouritsen-Frost flight simulator (3, 4, 10). We first examined tethered migrants housed in the laboratory under two 12-hours-lights: 12-hours-dark lighting conditions.

This was shown by analyzing the circadian timing of adult eclosion behavior. Newly formed pupae were exposed to one of two light:dark cycles, which differed in phase from each other by 6 hours, in which all light was filtered through the UV-interference filter. Circadian entrainment to the two lighting cycles that lacked UV light was evaluated by placing the pupae in constant darkness as the animals became mature enough to eclose. For each group, animals eclosing in constant darkness did so during the early portion of what would have been the light period of the lighting cycles (Fig. 3D). The mean peak times of eclosion, as monitored for 2 days in constant darkness, differed between the two groups by 5.5 hours (as compared with the 6.0-hour shift of the lighting cycles) (Fig. 3D). The data indicate that the circadian clock was properly entrained by light of a wavelength _394 nm (17). Our results provide insights into time-compensated

Sun compass navigation in migratory monarch butterflies. The necessity for circadian control for the time-compensation component of monarch navigation shows that a functioning clock is essential for successful migration. Moreover, the molecular gears of the monarch circadian clock (such as per) are likely the first identified genetic components underlying migratory behavior. Examination of the lighting requirements for time-compensated Sun compass navigation suggests that there are distinct light-input pathways for the stimulation of oriented flight behavior (UV-dependent) and entrainment of the circadian clock (UV-independent).

Tracing these pathways into the brain should aid our understanding of the clock-compass interface and further illuminate the mechanisms of monarch butterfly migration.

The present data show uncoupling of leading-and lagging-strand synthesis, implying the continuation of fork opening despite a block in one strand. Uncoupling of simultaneous strand synthesis may occur without disruption of the diametric Pol III core assembly.

When the lesion resides in the lagging strand, a new priming event may enable lagging- strand synthesis to continue, generating a gapped plasmid and a complete double stranded plasmid molecule from lagging and leading strands, respectively. When the block resides in the leading strand, the lagging strand Pol III core gets ahead of the leading strand core, generating a complete double stranded plasmid from the lagging strand. A partially double-stranded molecule with a single-stranded region (_1 kb) extending from the lesion site to the end of the plasmid is formed from the leading strand. Plasmids of larger size will be required to determine how far DnaB helicase can travel before the whole fork stops. In both orientations, TLS can repair the partially replicated molecule with similar efficiency and a 50-min delay.

This delay strongly depends on the chemical nature of the blocking lesion (8). Alternatively, the partially replicated intermediates may be processed by regressed fork formation

(10–13). In E. coli and in yeast, genetic data have indicated the bypass of specific lesions to require multiple polymerase switches and specific combinations of TLS polymerases

(7, 14–21). The strategy implemented here will be useful to unravel the complex biochemistry of various TLS pathways in vivo, thus providing a powerful complement to in vitro approaches.

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