A Transmission Model for the Ecology of an Avian Blood Parasite in a Temperate Ecosystem

<div><p>Most of our knowledge about avian haemosporidian parasites comes from the Hawaiian archipelago, where recently introduced <i>Plasmodium</i><i>relictum</i> has contributed to the extinction of many endemic avian species. While the ecology of invasive malaria is reasonably understood, the ecology of endemic haemosporidian infection in mainland systems is poorly understood, even though it is the rule rather than the exception. We develop a mathematical model to explore and identify the ecological factors that most influence transmission of the common avian parasite, <i>Leucocytozoonfringillinarum</i> (Apicomplexa). The model was parameterized from White-crowned Sparrow (<i>Zonotrichia</i><i>leucophrys</i>) and <i>S. silvestre</i><i> / craigi</i> black fly populations breeding in an alpine ecosystem. We identify and examine the importance of altricial nestlings, the seasonal relapse of infected birds for parasite persistence across breeding seasons, and potential impacts of seasonal changes in black fly emergence on parasite prevalence in a high elevation temperate system. We also use the model to identify and estimate the parameters most influencing transmission dynamics. Our analysis found that relapse of adult birds and young of the year birds were crucial for parasite persistence across multiple seasons. However, distinguishing between nude nestlings and feathered young of the year was unnecessary. Finally, due to model sensitivity to many black fly parameters, parasite prevalence and sparrow recruitment may be most affected by seasonal changes in environmental temperature driving shifts in black fly emergence and gonotrophic cycles.</p> </div

Parasite prevalence in the sparrow population peaks twice during the breeding season.

<p>In 2005, parasite prevalence of <i>L</i>. <i>fringillinarum</i> (solid line; likely comprising acute, relapsing, and chronic infections) peaks twice throughout the breeding season (day 30 equals May 30^th). The first peak corresponds prior to the date of peak nestling hatching and black fly emergence (vertical dotted lines). Based on when they occur during the season, the first and second prevalence peaks most likely correspond to relapsing infectious adult and newly infected first year birds, respectively. Cumulative parasite prevalence indicates that the end of the season parasite prevalence in the sparrow population is 30% in 2005 (dashed line).</p

Extensions of the simple model.

<p>The multi-year model adds a relapsing infectious adult bird compartment and <i>ovens</i> (dashed compartments), which represent overwintering birds in various states (adult or first year birds that are susceptible or latently infected). Arrows denote flows of individuals entering or leaving compartments within each module over time. <b><i>B</i></b> and <b><i>F</i></b> in the module headings represent the total number of individuals in the bird and black fly vector populations, respectively. The first one or two letters of each compartment label corresponds to the infection status of individuals entering or leaving that compartment (<b><i>S</i></b> = susceptible, <b><i>E</i></b> = exposed, <b><i>I</i></b> = acutely infectious, <b><i>CI</i></b> = chronically infectious, <b><i>RI</i></b> = relapsing infectious, and LI = latently infected). Subscripts in each compartment label corresponds to the population the module represents (<b><i>N</i></b> = nude nestling and <b><i>J</i></b> = feathered first year birds, <b><i>A</i></b> = adult bird population, and <b><i>F</i></b> = black fly vector population). In the multi-year model model, <b><i>P</i></b> is now equal to the sum of [<i>b</i>_<i>A</i> (<i>I</i>_<i>A</i> + <i>I</i>_<i>J</i>) + <i>b</i>_<i>C</i> (<i>CI</i>_<i>A</i> + <i>CI</i>_<i>J</i>) + <i>b</i>_<i>R</i><i>RI</i>_<i>A</i>] / <i>B</i>. To ensure approximately all susceptible, chronically infectious, and relapsing infectious birds transition into the corresponding overwinter oven, we added chains or compartments to these stages (chains = <i>S</i>_<i>J</i>: 15; <i>S</i>_<i>A</i>: 25; <i>CI</i>_<i>J</i> and <i>CI</i>_<i>A</i>: 4; <i>RI</i>_<i>A</i>: 20). To ensure all black flies were dead by the end of the breeding season, we added four chains to the infectious black fly class (I_F). Initial conditions for the compartments in the modules are the following: 100 sparrows begin as susceptible adults (S_A) and 100 sparrows enter as relapsing infectious adults (RI_A). All other compartments initially begin with zero individuals.</p

Field Autotomy Sex Data

This data file contains field autotomy sex data for all of our study locations where we collected field autotomy data

Earlier black fly emergence increases parasite prevalence in sparrow and vector populations.

<p>As suggested by empirical data, <i>q</i>_<i>F</i> was initially set at day 66 (July 5th). We then shifted <i>q</i>_<i>F</i> earlier (day 0, May 1st) and later (day 120, August 28^th) in the season. Both final prevalence of infected birds and mean prevalence of infectious black flies was highest when <i>q</i>_<i>F</i> was set to day 0 because this maximized the degree of overlap between susceptible first year birds and infectious black flies.</p

Hierarchical Linear Model - Flight Initiation Distance

This file contains flight initiation distance dat from all of our study locations. These data were used to construct models of FID

Donihue et al. 2015 Feed or Fight Data

All data archived here were used for analyses in Donihue et al. "Feed or Fight: Testing the impact of food availability and intraspecific aggression on the functional ecology of an island lizard." Data is in five worksheets. Please see ReadMe file for additional information

Detection Distance - Flight Initiation Distance

This data file contains detection distance data for analysis of flight initiation distance

data_final

data_fina

Belasen et al. CTmax

Sites are coded as follows: 1 - Naxos Low Elevation (NLE); 2 - Naxos South-Facing (NSF); 3 - Naxos North-Facing (NNF); 4 - Ovriokastro, Small Islet 1 (OVR); 5 - Aspronissi, Small Islet 2 (ASP); Max temp is the maximum temperature at which a lizard could right itself during a laboratory righting test; weight is the weight of the lizard in grams; SVL is the snout-vent length of the lizard in centimeter