Fecundity-size relationships overlapped between recent and historic collections.

<p>Values here are for pre-spawning females in the Connecticut River (2015)–collected in the lower river (plus [+] symbol) or the Hadley Falls Power Station (cross [×])–compared to two historic data sets: A) pre-spawning females sampled from the Hudson River 1951 (dots [.], data from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.ref006" target="_blank">6</a>]); B) and predictive, linear model parameters reported for three rivers as sampled in the 1960s: York River, Virginia (dashed, thin line), Connecticut River (solid, thick line), and St. John River, Canada (dotted, thin line) (parameters from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.ref027" target="_blank">27</a>]; table 30). In (B), raw data were not included in Leggett [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.ref027" target="_blank">27</a>], fork length was measured in cm, and fecundity was not log-transformed (compare to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.g007" target="_blank">Fig 7A</a>).</p

A sequence of oocyte stages depicting the transition from primary to secondary oocytes.

<p><b>A.</b> Perinucleolar (PE)–thin chorion, no cytoplasmic inclusions; nucleoli visible around periphery of nucleus (arrow). <b>B.</b> Early cortical alveolar (C1)–thin chorion; tiny clear inclusions appear around cytoplasm (arrow). <b>C, D.</b> Late cortical alveolar (C2)–chorion thickening; dark inclusions appear within the white inclusions of the cytoplasm (arrow). Image D is more advanced; the cortical alveoli grow larger and proximally. <b>E.</b> Early vitellogenesis (V1)–first sign of yolk (red) inclusions appear (arrow). As the cell grows, yolk continues to fill the cytoplasm. <b>F.</b> Cell is still staged as V1 as long as yolk has not expanded to the distal edge of the cytoplasm. Black scale bar: images A–E bar = 50 <b>μ</b>m; image F bar = 250 <b>μ</b>m.</p

Yolked Oocyte Dynamics Support Agreement between Determinate- and Indeterminate-Method Estimates of Annual Fecundity for a Northeastern United States Population of American Shad

<div><p>Reports of American shad fecundity identify two important themes regarding egg production in fishes. First, geographic variation occurs and is biologically meaningful. Shad annual fecundity decreases with increasing latitude, but predicted lifetime fecundity does not, because of a counter-gradient of survival probability, all of which can explain the adaptive significance of natal homing. Second, the appropriate method of measuring fecundity depends on the pattern of oocyte development. Historically, the relatively simple determinate-fecundity method was used; however, a recent study in a Virginia river indicates that this method may be biased, requiring the more complicated indeterminate method. We address both themes with collections from the 2015 shad spawning run in the Connecticut River, USA. Criteria for using a determinate method were satisfied for this northern population: 1) a size gap evident in the oocyte size frequency distribution, indicating group-synchronous development of yolked oocytes; 2) a decline, early in spawning, in the standing stock of yolked oocytes; and 3) low levels of atresia at the end of spawning. The determinate-method estimate of American shad annual (2015) fecundity (303,000 ± 73,400; mean ± sd) overlapped historic estimates for this and a neighboring river. The indeterminate-method estimate of annual (2015) fecundity (311,500 ± 4,500 sd) was not significantly different from the determinate-method estimate (Student’s t-test, P > 0.05). In contrast, indeterminate-method estimates of annual fecundity for a Virginia population were twice as high as that measured by the determinate method in the past. This can all be explained by fundamentally different patterns of oogenesis (i.e., group synchrony versus asynchrony with respect to yolk development) at different latitudes. American shad, which is distributed within its native range from the Canadian maritimes to Florida, USA (50–30°N), may be particularly well suited to evaluate intra-specific variation in oocyte development, a relatively unexplored life history trait.</p></div

Histograms of oocyte diameters from six downstream migrating, female American shad collected from the Connecticut River in 2015.

<p>Fish on the left (panels A-C) were spent, whereas fish on the right were resting (D-F). At least one sample of both maturity classes shown were collected on both June 18 at Hadley Falls Power Station and June 30 at Cabot Power Station. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.t002" target="_blank">Table 2B</a> for more details about each fish. Colors and hatching identifying each growth phase are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.g004" target="_blank">Fig 4</a>.</p

The decreasing trend in potential annual fecundity with increasing latitude, as observed previously with the determinate fecundity method, persists for the two rivers analyzed with the indeterminate fecundity method.

<p>This figure compares determinate fecundity estimates from Leggett and Carscadden [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.ref028" target="_blank">28</a>], indeterminate fecundity estimate for the York River from Hyle et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.ref014" target="_blank">14</a>], and new indeterminate fecundity estimate for the Connecticut River from the current study (new determine fecundity estimate not shown).</p

Histograms of oocyte diameters from six upstream migrating, female American shad collected from the Connecticut River in 2015 (one fish per panel).

<p>All females were developing (Class A). Fish in panels A-C were collected by gill net in the lower river, whereas fish in panels D-F were collected at three different power stations: Vernon (D), Cabot (E), and Hadley Falls (F). See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.t002" target="_blank">Table 2A</a> for more details about each fish. Colors are transparent and overlaid (not stacked), corresponding to small, transparent oocytes (red; primary growth phase), medium, translucent oocytes (yellow; transitional growth phase), and larger, opaque oocytes (green; secondary growth phase). Angled hatching is overlaid on the yellow bars to distinguish them more. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.t001" target="_blank">Table 1</a> for additional details about phases of development.</p

Estimation of potential annual fecundity, as measured by a determinate fecundity method, relative to fish size (log-log transformation).

<p>The size-specific estimate decreases once a fish shows evidence of spawning (see text). The four sampling events and associated correlation coefficients are: A) pre-spawning fish in the lower river (April 30–May 6, <i>r</i> = 0.36, <i>n</i> = 25, <i>P</i> = 0.08), B) pre-spawning fish collected at Hadley Falls Power Station (May 12, <i>r</i> = 0.65, <i>n</i> = 20, <i>P</i> = 0.002), C) spawning fish collected at Hadley Falls and Cabot Power Stations (May 12–13, <i>r</i> = 0.63, <i>n</i> = 11, <i>P</i> = 0.04), and D) spawning fish collected at Hadley Falls and Vernon Power Stations (May 19–20, <i>r</i> = 0.41, <i>n</i> = 10, <i>P</i> = 0.2). Individual fish are plotted as dots, the predictive regression is a blue line, and the 95% confidence limits are enclosed in solid gray.</p

Box-whisker plots of oocyte sizes, as measured from histology preparations.

<p>For each of ten oocyte stages (see text and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.t001" target="_blank">Table 1</a> for full stage descriptions), the data are represented by a thick horizontal line (median), a box (25–75^th percentile), whiskers (range), and any outliers (then the whiskers are roughly the 95% confidence limits). The lower (dotted) horizontal line corresponds to the size (100 μm) of the primary growth (‘anlagen’) oocytes, and the upper (dashed) line corresponds to the lower size (400 μm) of vitellogenic oocytes, as reported by Lehman [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.ref006" target="_blank">6</a>] and assumed by others (e.g., [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.ref012" target="_blank">12</a>]). Values along the top axis are numbers of cells measured by stage. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.g002" target="_blank">Fig 2</a> for images of the first four stages.</p

Characteristics of whole oocytes, by phase of development, and corresponding histology stages.

<p>Appearance is as under transmitted light. Sizes are approximate (100 μm). See text and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164203#pone.0164203.g002" target="_blank">Fig 2</a> for description of histology stages.</p

Profiles of <i>chl a</i> concentration measured in sites L1129b (panel a) and L1105 (panel b).

<p>The black lines have been obtained by connecting the experimental points corresponding to samples distanced of 1 meter along the water column. The total number of samples measured in the two sites is for L1129b, and for L1105. (Courtesy of Denaro et al., 2013 (Ref. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066765#pone.0066765-Denaro1" target="_blank">[28]</a>)).</p